Publications

2013

• Intégrale invariante pour la propagation de fissure en élastoplasticité sous chargement de fatigue
  
  • Riolo Vincent
  • Chiaruttini Vincent
  • Guilié Joachim
  • Feyel Frédéric
  , 2013. Afin d'étendre les approches issues de la mécanique linéaire de la rupture aux cas des matériaux standards généralisés et prendre en compte des effets liés aux phénomènes de plasticité, on se propose d'étudier une grandeur énergétique globale, calculée par une intégrale invariante. Une première étude numérique du comportement asymptotique de cette grandeur est menée sur des matériaux élasto-plastique à écrouissage cinématique ou isotrope. Une stratégie basée sur l'introduction d'une longueur interne est alors proposée de façon à montrer qualitativement l'intérêt d'une telle approche pour alimenter une loi de propagation en fatigue permettant de prendre en compte les effets d'histoire en front de fissure. Enfin une application en propagation 2D montrant l'influence des effets de surcharges est présentée.
• Formulation d'un élément coque en analyse isogéométrique pour la simulation du choc
  
  • Adam Cédric
  • Bouabdallah Salim
  • Zarroug Malek
  • Maitournam Habibou
  , 2013. Dans cet article, nous proposons, pour l'analyse isogéométrique, un modèle de coque tridimensionnel dégénéré basé sur une cinématique du premier ordre dans l'épaisseur avec prise en compte du cisaillement transversal (théorie de Reissner-Mindlin). Nous examinons diverses approches pour la description de la géométrie et nous les comparons sur des cas tests linéaires et non-linéaires. Le résultats présentés sont comparés à ceux obtenus avec un modèle volumique ainsi qu'aux solutions de référence données dans la bibliographie.
• On the identification of nonlinear behavior of highly filled elastomers
  
  • Jalocha Dimitri
  • Azoug Aurélie
  • Constantinescu Andrei
  • Nevière Robert
  , 2013. Solid propellants are highly filled elastomers used as propulsion medium. Because of the high volume filler fraction of 80% − 90%, several sizes of fillers are used and as a consequence of the complex microstructure the material presents important nonlinearities in the macroscopic behavior. An abrupt increase in the viscoelastic storage and loss modulus has been experimentally observed in [2]. The objective of this paper is to explore numerically a highly filled elastic composite under the assumptions of "rigid" fillers, an elastic matrix and large strains. The present numerical analysis is based on several artificially created microstructures. The results show the influence of the material behavior of the matrix on the global stiffness. The computed mechanical response is in agreement with experiment observations. The mechanical response of the composite under a uniaxial loading presents a linear and a nonlinear part. Both are analyzed to understand the microstructural effects that lead to the macroscopic behavior. The apparent modulus of the linear part increases with respect to the volume fraction of fillers and the stiffening effect occurring in the nonlinear part is not dependent of the matrix behavior.
• Continuum electromechanical theory for nematic continua with application to Freedericksz instability
  
  • Pampolini Giampiero
  • Triantafyllidis Nicolas
  , 2013. In this communication we present the work by Pampolini and Triantafyllidis [1], in which an electro-mechanical theory for nematic continua is proposed. The theory is based on a variational approach and the equilibrium relations plus the Maxwell's equations are obtained as the Euler-Lagrange equations of a specific potential energy. The variational formulation is applied to the study of a 2D boundary value problem, termed in the literature as Freedericksz transition, where a nematic liquid crystal layer is confined between two plates and an electric field is applied perpendicular to the plates. This boundary value problem is treated as a bifurcation problem and an asymptotic analysis of the bifurcated equilibrium path is carried out. (10.1007/s10659-017-9665-y)
  DOI : 10.1007/s10659-017-9665-y
• Modélisation multi-échelle du comportement des câblés textiles
  
  • Attia Houda
  • Durville Damien
  • Le Tallec Patrick
  , 2013. Une stratégie multi-échelle est proposée pour aborder la simulation de câblés textiles à grands nombres de filaments, en vue de déterminer le comportement global de ces structures tout en approchant les sollicitations locales subies à l'échelle des filaments. Cette stratégie repose sur le développement d'un modèle simplifié de macro-fibres pour résoudre le problème à l'échelle macroscopique, et la formulation d'un problème à l'échelle microscopique piloté par des quantités pertinentes déterminées à l'échelle macroscopique. Les paramètres du modèle macroscopique sont recalés de manière à obtenir un accord entre les densités déterminées aux échelles macroscopique et microscopique. Dans un premier temps, le cadre de l'étude a été simplifié en se ramenant à un problème 2D. On présente alors dans cet article une illustration 2D de l'approche multi-échelle proposée.
• Calcul direct de la raideur non linéaire géométrique pour la réduction de modèles de coques en éléments finis
  
  • Touzé Cyril
  • Vidrascu Marina
  • Chapelle Dominique
  , 2013. Les vibrations non linéaires géométriques de coques minces, discrétisées par éléments finis sont considérées. Dans le but de réduire la dynamique vibratoire à des modèles comprenant un petit nombre de degrés de liberté, la base des modes propres linéaires est utilisée. La projection fait alors apparaitre un ensemble de coefficients de couplage non linéaires quadratiques et cubiques. Une méthode directe permettant le calcul de ces coefficients est proposée et implémentée. Une fois le modèle projeté, des études de bifurcation de solutions périodiques sont possibles a moindre coût, ce qui permet de calculer les branches stables et instables des solutions libres et forcées.
• Motion of a spherical capsule in simple shear flow: influence of the bending resistance
  
  • Dupont Claire
  • Salsac Anne-Virginie
  • Barthes-Biesel Dominique
  • Vidrascu Marina
  • Le Tallec Patrick
  , 2013. We simulate the motion of an initially spherical capsule in a simple shear flow in order to determine the influence of the bending resistance on wrinkle formation on the membrane. We use a numerical method coupling a nonlinear shell finite element method for the capsule wall mechanics with a boundary integral method to solve the Stokes equation. The capsule wall is discretized with MITC linear triangular shell finite elements. We find that, at low flow strength, buckling occurs in the central region of the capsule. The number of wrinkles on the membrane decreases with the bending stiffness and above a critical value, wrinkles no longer form. For thickness to radius ratios below 5%, the bending stiffness does not have any significant effect on the overall capsule motion and deformation. The mean capsule shape is identical whether the wall is modeled as a shell or a two-dimensional membrane, which shows that the dynamics of thin capsules is mainly governed by shear elasticity and membrane effects.
• High strain rate biaxial testing of sheet materials
  
  • Grolleau Vincent
  • Galpin Bertrand
  • Penin Arnaud
  • Mohr Dirk
  • Rio Gérard
  • Gary Gerard
  , 2013. Rate dependent constitutive models are widely used in sheet metal forming and crash simulations. In these applications, the material is subjected to large deformations at strain rates of up to 1000/s. In addition, the stress state is seldom uniaxial and of multi-axial nature instead. It is the aim of this work to investigate the effect of stress state on the strain rate sensitivity of some BCC and FCC metals. The dynamic bulge testing cell for split Hopkinson pressure bar systems is used to perform high strain rate biaxial tensile tests on sheet metal. The original idea is to make use of the input bar to apply and measure the fluid pressure in the bulging experiment. Detailed finite element models of the testing systems are used to simulate all experiments and the parameters of the rate-dependent plasticity model are then identified through inverse analysis.
• Personalization of a Cardiac Electromechanical Model using Reduced Order Unscented Kalman Filtering from Regional Volumes
  
  • Marchesseau Stéphanie
  • Delingette Hervé
  • Sermesant Maxime
  • Cabrera Lozoya Rocio
  • Tobon-Gomez Catalina
  • Moireau Philippe
  • Figueras I Ventura Rosa Maria
  • Lekadir Karim
  • Hernandez Alfredo
  • Garreau Mireille
  • Donal Erwan
  • Leclercq Christophe
  • Duckett Simon G.
  • Rhode Kawal
  • Rinaldi Christopher Aldo
  • Frangi Alejandro F.
  • Razavi Reza
  • Chapelle Dominique
  • Ayache Nicholas
  Medical Image Analysis, Elsevier, 2013, 17 (7), pp.816-829. Patient-specific cardiac modelling can help in understanding pathophysiology and therapy planning. However it requires to combine functional and anatomical data in order to build accurate models and to personalize the model geometry, kinematics, electrophysiology and mechanics. Personalizing the electromechanical coupling from medical images is a challenging task. We use the Bestel-Clément-Sorine (BCS) electromechanical model of the heart, which provides reasonable accuracy with a reasonable number of parameters (14 for each ventricle) compared to the available clinical data at the organ level. We propose a personalization strategy from cine MRI data in two steps. We first estimate global parameters with an automatic calibration algorithm based on the Unscented Transform which allows to initialize the parameters while matching the volume and pressure curves. In a second step we locally personalize the contractilities of all AHA (American Heart Association) zones of the left ventricle using the Reduced Order Unscented Kalman Filtering on Regional Volumes. This personalization strategy was validated synthetically and tested successfully on eight healthy and three pathological cases. (10.1016/j.media.2013.04.012)
  DOI : 10.1016/j.media.2013.04.012
• An improved Lagrangian thermography procedure for the quantification of the temperature fields within polycrystals
  
  • Seghir Rian
  • Witz Jean-Francois
  • Bodelot Laurence
  • Charkaluk Eric
  • Dufrenoy Philippe
  Quantitative InfraRed Thermography Journal, Taylor and Francis, 2013, 10 (1), pp.74-95. Polycrystalline metallic materials are made of an aggregate of grains more or less well oriented with respect to the loading axis. During mechanical loading, the diversity of grain orientations leads to a heterogeneous deformation at the local scale. It is well known that most of the plastic work generated during the deformation process reappears in the form of heat, whereas a certain proportion remains latent in the material and is associated with microstructural changes. To access the local stored energy during deformation processes, experimental energy balances are needed at a suitable scale. Thus, simultaneous measurements of thermal and kinematic fields were made in-house at the microstructural scale of a 316L stainless steel submitted to a macroscopic monotonic tensile test. The aim of the present study is to propose a complete calibration strategy allowing us to estimate the thermal variations of each material point along its local and complex deformation path. This calibration strategy is a key element for achieving experimental granular energy balances and has to overcome two major experimental problems: the dynamics of each infrared focal plane array sensor that leads to undesired spatial and temporal noise and the complexity of the local loading path that must be captured by simultaneous complementary measurement. The improvement of such a multifield strategy is crucial for performing properly the experimental and local energy balances required to build new energetically based damage criteria. (10.1080/17686733.2013.785207)
  DOI : 10.1080/17686733.2013.785207
• Domain decomposition and multi-scale computations of singularities in mechanical structures
  
  • Dang Thi Bach Tuyet
  , 2013. A major issue in fracture mechanics is to model the nucleation of a crack in a sound material. There are two difficulties: the first one is to propose a law able to predict that nucleation; the second is a purely numerical issue. It is indeed difficult to compute with a good accuracy all the mechanical quantities like the energy release rate associated with a crack of small length which appears at the tip of a notch. The classical finite element method leads to inaccurate results because of the overlap of two singularities which cannot be correctly captured by this method: one due to the tip of the notch, the other due to the tip of the crack. A specific method of approximation based on asymptotic expansions is preferable as it is developed in analog situations with localized defects. The first chapter of the thesis is devoted to the presentation of this Matched Asymptotic Method (shortly, the MAM) in the case of a defect (which includes the case of a crack) located at the tip of a notch in the simplified context of antiplane linear elasticity. The main goal of the thesis is to use these asymptotic methods to predict the nucleation or the propagation of defects (like cracks) near those singular points. The second chapter of the thesis will be devoted to this task. This requires, of course, to overcome the first issue by introducing a criterion for nucleation. This delicate issue has not received a definitive answer at the present time and it was considered for a long time as a problem which could not be solved in the framework of Griffith theory of fracture. The main invoked reason is that the release of energy due to a small crack tends to zero when the length of the crack tends to zero. Therefore, if one follows the Griffith criterion which stands that the crack can propagate only when the energy release rate reaches a critical value characteristic of the material, no nucleation is possible because the energy release rate vanishes when there is no preexisting crack. This "drawback" of Griffith's theory was one of the motivations which led Francfort and Marigo to replace the Griffith criterion by a principle of least energy. It turns out that this principle of global minimization of the energy is really able to predict the nucleation of cracks in a sound body. However, the nucleation is necessarily brutal in the sense that a crack of finite length suddenly appears at a critical loading. Moreover the system has to cross over an energy barrier which can be high when the minimum is "far". Another way to overcome the issue of the crack nucleation is to leave the pure Griffith setting by considering cohesive cracks. Indeed, since any cohesive force model contains a critical stress, it becomes possible to nucleate crack without invoking global energy minimization. Accordingly, we propose to revisit the problem of nucleation of a crack at the tip of a notch by comparing the three criteria. One of our goal is to use the MAM to obtain semi-analytical expressions for the critical loading at which a crack appears and the length of the nucleated crack. Specifically, the thesis is organized as follows. Chapter 1 is devoted to the description of the MAM on a generic anti-plane linear elastic problem where the body contains a defect near the tip of a notch. We first decompose the solution into two expansions: one, the outer expansion, valid far enough from the tip of the notch, the other, the inner expansion, valid in a neighborhood of the tip of the notch. These expansions contain a sequence of inner and outer terms which are solutions of inner and outer problems and which are interdependent by the matching conditions. Moreover each term contains a regular and a singular part. We explain how all the terms and the coefficients entering in their singular and regular parts are sequentially determined. The chapter finishes by an example where the exact solution is obtained in a closed form and hence where we can verify the relevance of the MAM. In Chapter 2, the MAM is applied to the case where the defect is a crack. Its main goal is to compute with a good accuracy the energy release rate associated with a crack of small length near the tip of the notch. Indeed, it is a real issue in the case of a genuine notch (by opposition to a crack) because the energy release rate starts from 0 when the length of the nucleated crack is 0, then is rapidly increasing with the length of the crack before reaching a maximum and finally is decreasing. Accordingly, after the setting of the problem, one first explains how one computes the energy release rate by the FEM and why the numerical results are less accurate when the crack length is small. Then, one uses the MAM to compute the energy release rate for small values of the crack length and one shows, as it was expected, that the smaller the size of the defect, the more accurate is the approximation by the MAM at a certain order. It even appears that one can obtain very accurate results by computing a small number of terms in the matched asymptotic expansions. We discuss also the influence of the angle of the notch on the accuracy of the results, this angle playing an important role in the process of nucleation (because, in particular, the length at which the maximum of the energy release rate is reached depends on the angle of the notch). It turns out that when the notch is sufficiently sharp, i.e. sufficiently close to a crack, it suffices to calculate the first two non trivial terms of the expansion of the energy release rate to capture with a very good accuracy the dependence of the energy release rate on the crack length. Then a cohesive model, the so-called Dugdale model, is considered in the last section of the chapter. Combining the MAM with the G method allows us to calculate in an almost closed form the nucleation and the evolution of the crack, namely the relations between the external load and the lengths of the non-cohesive zone and the cohesive zone. Specifically, it turns out that the inner problem can be seen as an Hilbert problem which can be solved with the help of complex potentials. Thus, the access to the solution is reduced to a few quadratures which are computed numerically. One obtains so an analytical expression of the critical load at which a "macroscopic" crack will appear in the body after an unstable stage of propagation of the nucleated crack. The order of magnitude of that critical load is directly associated with the power of the singularity of the solution before nucleation which is itself a known function of the angle of the notch. Chapter 3 proposes a generalization of all the previous results in the plane elasticity setting. Specifically, the goal is still to study the nucleation of non cohesive or cohesive cracks at the angle of a notch in the case of a linearly elastic isotropic material but now by considering plane displacements. Moreover, we will consider as well pure mode I situation as mixed modes cases. In the first part of the chapter we use the global minimization principle in the case of a non cohesive crack. In the second part we consider Dugdale cohesive force model. In both cases the MAM is used to compensate the non accuracy of the finite element method. All the derived results can be seen as simple generalizations of those developed in the antiplane case. Indeed, from a conceptual and qualitative viewpoint, we obtain essentially the same types of properties. However, from a technical point of view, the MAM is more difficult to apply in plane elasticity because the sequence of singularities can be obtained only by solving transcendental equations. Therefore, the numerical procedure becomes more expansive. Moreover, from the analytical point of view, the calculations become much more intricate and consequently a part of these calculations are given in the appendix.
• Interfacial adhesion between the iron fillers and the silicone matrix in magneto-rheological elastomers at high deformations
  
  • Pössinger Tobias
  • Bolzmacher Christian
  • Bodelot Laurence
  • Triantafyllidis Nicolas
  , 2013, 8763, pp.87631Y-11. This work investigates the interfacial adhesion between the iron fillers and the silicone matrix in magneto-rheological elastomers at high deformations. Carbonyl iron powder, composed of mechanically soft spherical particles with a median size of 3.5 μm and a volume concentration of 3.5%, was mixed in a soft silicone matrix (Shore 00-20); the compound was then degassed and cured under temperature. The presence of a homogeneous magnetic field of 0.3 T during the curing process allowed the formation of particle chains. Tensile tests of these samples under scanning electron microscope showed interfacial slipping and debonding between the two phases. To improve interfacial adhesion, a silane primer was applied to the iron particles, following two different procedures, before the mixing and crosslinking process, thus giving two additional types of samples. In tensile testing lengthwise to the particle alignment, with engineering strains up to 150%, the structural responses of the different types of samples were compared. An enhanced adhesion of the iron fillers to the silicone matrix resulting in a reinforced matrix and increased tensile strength during the first loading path could be observed. Furthermore, scanning electron microscope images show that a more elaborated particle-matrix interface was obtained with the primer additive. (10.1117/12.2016532)
  DOI : 10.1117/12.2016532
• A simplified solution for Gas Flow during a Blow-out in an H2 or air storage cavern
  
  • Berest Pierre
  • Djakeun-Djizanne Hippolyte
  • Brouard Benoît
  • Frangi Attilio
  , 2013, pp.125-144. A small number of blow-outs from gas storage caverns (for example, in Moss Bluff, Texas and Fort Saskatchewan, Canada) have been described in the literature. Gas flow lasted several days before the caverns were empty. In this paper, we suggest simplified methods that allow for computing blow-out duration and evolution of gas temperature and pressure in the cavern and in the well. This method is used to compute air flow from a shaft mine, an accident described by Van Sambeek (2009). The case of a hydrogen storage cavern also is considered, as it is known that hydrogen depressurization can lead, in certain cases, to hydrogen temperature increase.
• Symbolic and numerical solution of the axisymmetric indentation problem for a multilayered elastic coating
  
  • Constantinescu Andrei
  • Korsunsky Alexander M.
  • Pison Olivier
  • Oueslati Abdelbacet
  International Journal of Solids and Structures, Elsevier, 2013, 50 (18), pp.2798-2807. This paper is concerned with a semi-analytical approach to the solution of the axisymmetric indentation problem for a multilayered elastic half-space. The stress and displacement fields for each layer and the substrate are derived in closed form by using the Papkovich-Neuber potentials and the Hankel transform. The bonded or sliding interface conditions between the sub-layers are handled by the use of the appropriate transfer matrix, and then the mixed boundary value problem is reduced to a Fredholm integral equation. Symbolic and numerical computations of the solution are implemented in the symbolic software Mathematica in the form of a fast and efficient numerical algorithm, allowing rapid determination of the load-displacement curves and composite elastic properties for an arbitrary rigid indenter shape. A series of results for different indenters (flat, conical, spherical and blunted conical punch shapes) and different multilayered composites is presented and discussed. The complete set of symbolic and numerical computations are provided as supplementary resources with the paper. (10.1016/j.ijsolstr.2013.04.017)
  DOI : 10.1016/j.ijsolstr.2013.04.017
• Réduction de modèle et simplification de l'intégration de loi de comportement pour la prévision de la durée de vie
  
  • Courtier Vivien
  , 2013. Dans le milieu aéronautique, la simulation numérique s'est largement imposée dans le développement industriel des systèmes complexes. De la conception au suivi en service, les simulations numériques sont nombreuses et variées. Afin de proposer des méthodes alternatives aux méthodes de calcul intensif, la réduction de modèle permet de réduire considérablement le coût de la résolution numérique des problèmes non linéaires en projetant les équations aux dérivées partielles sur une base réduite. De plus, la description des phénomènes physiques requiert une loi de comportement élaborée dont une simplification est considérée en exploitant une partie restreinte du domaine spatial. Les études effectuées ont pour but d'apporter certains développements à la méthode incrémentale et adaptative A Priori Hyper Reduction dans le cas des matériaux hétérogènes. Ces développements sont intégrés dans le code éléments finis Z-set et utilisés pour traiter une série d'exemples académiques sur des structures composites.
• Multiscale experimental investigation of crystal plasticity and grain boundary sliding in synthetic halite using digital image correlation
  
  • Bourcier Mathieu
  • Bornert Michel
  • Dimanov Alexandre
  • Héripré Eva
  • Raphanel Jean
  Journal of Geophysical Research : Solid Earth, American Geophysical Union, 2013, 118 (2), pp.511-526. There is a renewed interest in the study of the rheology of halite since salt cavities are considered for waste repositories or energy storage. This research benefits from the development of observation techniques at the microscale, which allow precise characterizations of microstructures, deformation mechanisms, and strain fields. These techniques are applied to uniaxial compression tests on synthetic halite done with a classical press and with a specific rig implemented in a scanning electron microscope. Digital images of the surface of the sample have been recorded at several loading stages. Surface markers allow the measurement of displacements by means of digital image correlation techniques. Global and local strain fields may then be computed using ad hoc data processing. Analysis of these results provides a measure of strain heterogeneity at various scales, an estimate of the size of the representative volume element, and most importantly an identification of the deformation mechanisms, namely crystal slip plasticity and grain boundary sliding, which are shown to be in a complex local interaction. Indeed, the applied macroscopic loading gives rise locally to complex stress states owing to relative crystallographic orientations, density and orientation of interfaces, and local deformation history. We have quantitatively estimated the relative importance of crystal slip plasticity and grain boundary sliding for different microstructures and evidenced their dependence on grain size. The two mechanisms of deformation and their link to the microstructure should thus be considered when modeling polycrystalline viscoplasticity. (10.1002/jgrb.50065)
  DOI : 10.1002/jgrb.50065
• Multiscale approach to the modelling of dense fibrous media based on the the development of an appropriate contact law at macroscopic scale
  
  • Attia Houda
  • Durville Damien
  • Ben Dhia Hachmi
  • Le Tallec Patrick
  , 2013.
• Modélisations multi-matériaux multi-vitesses en dynamique rapide
  
  • Folzan Gauthier
  , 2013. De nombreuses simulations dans les domaines des impacts, des interactions fluide-structure ou des écoulements multiphasiques impliquent différentes structures indépendantes interagissant entre elles à travers des interfaces complexes. Pour ces problèmes, les stratégies classiques utilisent souvent une approche lagrangienne utilisant un maillage éléments finis par structure et des stratégies de couplage et de mise en contact adéquates. Ceci est très coûteux en terme de génération de maillages et difficile à mettre en place en présence de grandes déformations. Une alternative est d'utiliser une stratégie " eulérienne " décrivant les différentes structures sur une grille unique en utilisant une vitesse moyenne unique et en développant des lois d'état ad hoc pour gérer le caractère multiphasique des éléments traversés par l'interface. La physique de l'interface de ces modèles est en générale assez grossière. Dans ce contexte, il y a un regain d'intérêt pour les modèles utilisant un maillage global unique non conforme avec les structures et définissant des champs de vitesses éléments finis indépendants pour décrire le mouvement de chacune des structures. Cette stratégie est intéressante mais induit différents problèmes : suivi d'interface, développement d'une formulation ALE adaptée car les matériaux et le maillage ont des vitesses différentes, traitement correct de la contrainte cinématique à l'interface entre les structures. Une grande attention doit être portée à ce dernier point pour proposer une approche stable, sans verrouillage numérique et restant robuste en cas de grandes déformations. Dans cette thèse, nous proposons une stratégie originale basée sur une méthode d'éléments finis enrichis. Elle définit un champ de vitesse éléments finis par matériau sur un unique maillage. Les différents champs se recouvrent et forment un champ enrichi qui peut avoir une discontinuité à l'interface et permet de décrire le glissement entre les matériaux. La discontinuité est contrôlée par une contrainte de continuité des vitesses normales et par une inconnue supplémentaire, la pression d'interface qui est le multiplicateur de Lagrange associé à la contrainte cinématique. La formulation ALE utilisée est basée sur une décomposition du pas de temps entre phase lagrangienne et phase de projection. La phase lagrangienne est résolue par le schéma de Wilkins classique des codes hydrodynamiques alors que la projection est réalisée par calcul d'intersection entre les maillages lagrangiens déformés par la matière et un maillage commun plus régulier. L'interface est construite à partir de la fraction volumique de chaque matériau et sa reconstruction peut être discontinue entre les éléments. Deux variantes sont introduites, analysées et comparées. Elles diffèrent par la discrétisation du multiplicateur de Lagrange et donc, par celle de la contrainte de vitesse : -la continuité par nœud utilise un multiplicateur défini aux nœuds. Cette variante est simple et rapide mais ne prend pas correctement en compte les différences de compressibilité entre matériaux, -la continuité par maille utilise un multiplicateur constant par segment d'interface. Cette variante donne des résultats meilleurs que la première version. La méthode est stabilisée par l'ajout de nœuds internes dans les mailles mixtes dont les fonctions bulles associés sont linéaires par morceaux dans chaque élément ainsi que par une condensation de la masse adaptée pour assurer un équilibre stable de l'interface. L'équation de mouvement du nœud interne est discrétisée par un schéma implicite en temps. En conséquence, nous devons résoudre un système couplant tous les nœuds de l'interface pour calculer les vitesses autour de l'interface. Les deux variantes ont été implantées dans un code industriel. Elles sont validées et comparées dans plusieurs cas tests impliquant diverses situations comme des interactions fluide-structure ou du glissement entre solides.
• Multiaxial fatigue models for short glass fiber reinforced polyamide - Part I: Nonlinear anisotropic constitutive behavior for cyclic response
  
  • Launay Antoine
  • Maitournam Habibou
  • Marco Yann
  • Raoult Ida
  International Journal of Fatigue, Elsevier, 2013, 47, pp.pp 382 - 389, issn = "0142-1123", url = "http://www.sciencedirect.com/science/article/pii/S014211231. Components made of short glass fiber reinforced (SGFR) thermoplastics are increasingly used in the automotive industry, and more frequently subjected to fatigue loadings during their service life. The determination of a predictive fatigue criterion is therefore a serious issue for the designers, and requires the knowledge of the local mechanical response under a large range of environmental conditions (temperature and relative humidity). As the cyclic behavior of polymeric material is reckoned to be highly nonlinear, even at room temperature, an accurate constitutive model is a preliminary step for confident fatigue design. The injection molding process induces a complex fiber orientation distribution (FOD), which affects both the mechanical response and the fatigue life of SGFR thermoplastics. This paper presents an extension of the constitutive behavior proposed by the authors in a previous work [Launay et al., Int J Plasticity, 2011], in order to take into account the influence of the local FOD on overall anisotropic elastic and viscoplastic properties. The proposed model is written in a general 3D anisotropic framework, and is validated on tensile samples with various FOD and loading histories: monotonic tensions, creep and/or relaxation steps, cyclic loadings. In Part II of this paper [Launay et al., Int J Fatigue, 2012], this constitutive model will be applied to the simulation of different fatigue samples subjected to multiaxial cyclic loadings. (10.1016/j.ijfatigue.2012.03.012)
  DOI : 10.1016/j.ijfatigue.2012.03.012
• Multiaxial fatigue models for short glass fibre reinforced polyamide. Part II: Fatigue life estimation
  
  • Launay Antoine
  • Maitournam Habibou
  • Marco Yann
  • Raoult Ida
  International Journal of Fatigue, Elsevier, 2013, 47, pp.pp 390 - 406, issn = "0142-1123", url = "http://www.sciencedirect.com/science/article/pii/S014211231. Components made of short fibre reinforced thermoplastics are increasingly used in the automotive industry, and more frequently subjected to fatigue loadings during their service life. The determination of a predictive fatigue criterion is therefore a serious issue for the designers, and requires the knowledge of the local mechanical response. As the cyclic behaviour of polymeric material is reckoned to be highly nonlinear, even at room temperature, an accurate constitutive model is a preliminary step for confident fatigue design. Constitutive equations for the cyclic behaviour, developed and validated by the authors in Part I of this paper [Launay et al., Int J Fatigue, in press], are applied to the mechanical analysis of fatigue campaigns carried out by Klimkeit et al. and De Monte et al. on specimens made out of polyamide 66 reinforced with 35 wt.% of short glass fibres. Both studies are performed at room temperature, with material conditioned at the equilibrium with air containing 50% of relative humidity (RH50) or dry-as-moulded (DAM). Post-processing the cyclic response in steady-state allows the comparison of several fatigue criteria. The fatigue databases involve various loadings, including the study of multiaxiality and mean-stress effects on different microstructures. Among all physical quantities, the dissipated energy density per cycle ΔWdiss displays the best correlation with the fatigue life. (10.1016/j.ijfatigue.2012.09.015)
  DOI : 10.1016/j.ijfatigue.2012.09.015
• Problèmes liés à l'abandon des cavernes souterraines de stockage d'hydrocarbures ou de production de saumure réalisées en formation salifère.
  
  • Berest Pierre
  , 2013. Problems raised by the long-term behavior of abandoned salt caverns are discussed.
• Vibroacoustics of the piano soundboard: (Non)linearity and modal properties in the low- and mid-frequency ranges
  
  • Ege Kerem
  • Boutillon Xavier
  • Rébillat Marc
  Journal of Sound and Vibration, Elsevier, 2013, 332 (5), pp.1288-1305. The piano soundboard transforms the string vibration into sound and therefore, its vibrations are of primary importance for the sound characteristics of the instrument. An original vibro-acoustical method is presented to isolate the soundboard nonlinearity from that of the exciting device (here: a loudspeaker) and to measure it. The nonlinear part of the soundboard response to an external excitation is quantitatively estimated for the first time, at ≈ -40 dB below the linear part at the ff nuance. Given this essentially linear response, a modal identification is performed up to 3 kHz by means of a novel high resolution modal analysis technique (Ege et al., High-resolution modal analysis, JSV, 325(4-5), 2009). Modal dampings (which, so far, were unknown for the piano in this frequency range) are determined in the midfrequency domain where FFT-based methods fail to evaluate them with an acceptable precision. They turn out to be close to those imposed by wood. A finite-element modelling of the soundboard is also presented. The low-order modal shapes and the comparison between the corresponding experimental and numerical modal frequencies suggest that the boundary conditions can be considered as blocked, except at very low frequencies. The frequency-dependency of the modal density and the observation of modal shapes reveal two well-separated regimes. Below ≈ 1 kHz, the soundboard vibrates more or less like a homogeneous plate. Above that limit, the structural waves are confined by ribs, as already noticed by several authors, and localised in restricted areas (one or a few inter-rib spaces), presumably due to a slightly irregular spacing of the ribs across the soundboard. (10.1016/j.jsv.2012.10.012)
  DOI : 10.1016/j.jsv.2012.10.012
• Onset of Failure in a Fiber Reinforced Elastomer Under Constrained Bending
  
  • Lignon Eric
  • Le Tallec Patrick
  • Triantafyllidis Nicolas
  International Journal of Solids and Structures, Elsevier, 2013, 50, pp.279 - 287. (10.1016/j.ijsolstr.2012.07.022)
  DOI : 10.1016/j.ijsolstr.2012.07.022
• Etude numérique des paramètres affectant les profils d'usure en fretting
  
  • Basseville Stéphanie
  • Proudhon Henry
  • Héripré Eva
  • Cailletaud Georges
  Matériaux et Techniques, EDP Sciences [1970-....], 2013, 101, pp.13 p.. L'étude est dédiée à l'endommagement lors d'un test numérique de fretting entre un cylindre et un plan. Un modèle d'usure s'appuyant sur un critère local énergétique permet de déterminer le profil d'usure dans différents contextes. La première simulation consiste à comparer des profils d'usure obtenus pour un matériau homogène lors d'un test d'usure unilatérale et d'un test d'usure bilatérale, i.e. chacune des surfaces de contact est usée. Dans la seconde simulation, un revêtement est pris en compte et présente un nombre important de pores. En leur présence, l'usure par abrasion est détectée et conduit naturellement à s'intéresser à la notion de troisième corps dans la zone de contact. Ainsi, une modélisation explicite des débris et la mise en œuvre du transfert de matière sont développés. Bien que la plasticité joue un rôle important dans les mécanismes d'endommagement, les simulations supposent un comportement élastique des matériaux en contact pour les tests (i) à (ii). Un dernier test permet d'aborder l'étude de l'effet d'une loi de comportement élasto-plastique pour le matériau usé. (10.1051/mattech/2013069)
  DOI : 10.1051/mattech/2013069
• Ductile deformation mechanisms of synthetic halite : a full field measurement approach
  
  • Dimanov Alexandre
  • Bourcier Mathieu
  • Heripre Eva
  • Bornert Michel
  • Raphanel Jean
  , 2013.