Publications

2013

• A Testing Technique of Confined Compression for Concrete at High Rates of Strain
  
  • Forquin Pascal
  • Gary G.
  • Gatuingt Fabrice
  , 2013. In order to characterise the behaviour of concrete under high pressures and high strain-rates, dynamic 1D-strain compression tests were performed. A cylindrical specimen is embedded in a steel confinement ring and compressed between 2 cylindrical plugs with a SHPB (Split Hopkinson Pressure Bars) device. Moreover, a new method was used to process the experimental data. It is based on numerical simulations of the cell loaded by an internal pressure that allow to build a relation between the pressure applied by the concrete to the inner surface of the cell and the external hoop strain measured by gauges. Stresses and strains in the specimen are computed at any loading time and the evolution of the deviatoric stress versus the pressure (deviatoric behaviour) and of the pressure versus volumetric strain (spherical behaviour) is deduced. The method is validated by several numerical simulations of the test involving different friction coefficients between the cell and the specimen. Three 1D-strain compression tests were performed and processed with the MB50 high-performance concrete. They showed that the deviatoric and spherical behaviours are almost independent of the strain rate in the observed range of strain rates (80-221 s-1). The deviatoric strength is seen to increase regularly with the hydrostatic pressure. The spherical behaviour indicates a fairly constant dynamic modulus of compressibility (around 5 to 6 GPa) up to a pressure of 900 MPa.
• Etude de l'amorçage en corrosion sous contrainte d'alliages à base de nickel soudés : influence des paramètres microstructuraux
  
  • Chaumun Elizabeth
  • Guerre Catherine
  • Héripré Eva
  • Sennour Mohamed
  • Crépin Jérôme
  • Duhamel Cecilie
  • Curières Ian De
  , 2013, pp.29-33.
• Effets du taux de déformation sur la rupture ductile des aciers à haute performance : Expériences et modélisation
  
  • Dunand Matthieu
  , 2013. L'industrie automobile emploie massivement les Aciers à Haute Performance (AHP) pour la fabrication des caisses en blanc, en raison de leur rapport résistance/masse élevé. Ils sont utilisés afin d'augmenter la sécurité des occupants en cas de crash, ou de réduire la masse du véhicule grâce à une diminution des sections utiles. En parallèle, le prototypage virtuel est omniprésent dans le processus de conception des nouveaux véhicules. En prenant l'exemple d'une caisse en blanc automobile, la conception de la structure globale et des procédés de mise en forme de ses composants nécessite des modèles prédictifs et fiables décrivant le comportement et la rupture des matériaux utilisés. Des efforts soutenus ont été entrepris ces cinq dernières années pour développer des modèles prédisant la rupture des AHP sous chargement statique. Pourtant les taux de déformations rencontrés lors d'opération de mise en forme sont de l'ordre de 10 s-1, et peuvent atteindre 103 s-1 lors de crashs. Le but de cette thèse est de développer une méthode fiable permettant d'évaluer l'influence du taux de déformation et de l'état de contrainte sur la rupture ductile d'AHP initialement non-fissurés. Une procédure expérimentale est conçue pour caractériser le comportement et l'initiation de la rupture dans des tôles chargées en traction à grande vitesse de déformation. La précision du dispositif est évaluée grâce à des validations numériques et expérimentales. Par la suite, une série d'expériences est réalisée à petite, moyenne et grande vitesse de déformation sur différents types d'éprouvettes de traction, afin de couvrir un spectre étendu d'états de contraintes. Une analyse détaillée de chaque expérience par la méthode des Éléments Finis permet de déterminer le trajet de chargement et l'état de déformation et de contrainte à la rupture dans chaque éprouvette, tout en prenant en compte les phénomènes de striction. La déformation à la rupture est significativement plus élevée à grande vitesse de déformation qu'à basse vitesse. De plus, les résultats montrent que l'influence du taux de déformation sur la ductilité ne peut pas être découplée de l'état de contrainte. Le modèle de comportement constitue un élément essentiel de cette approche hybride expérimentale-numérique. Un modèle de plasticité dépendant du taux de déformation est proposé pour prédire la réponse mécanique des AHP sur toute la plage de déformation, taux de déformation et état de contrainte couverte par le programme expérimental. La précision du modèle est validée par comparaison de mesures expérimentales globales et locales aux prédictions numériques correspondantes. De plus, l'influence de la discrétisation spatiale utilisée dans les simulations par Eléments Finis sur la précision de l'approche hybride expérimentale-numérique est quantifiée. Il est montré qu'un maillage fin d'éléments hexaédriques est nécessaire pour obtenir des prédictions précises jusqu'à la rupture. Ce type de maillage n'est pas compatible avec des applications industrielles à grande échelle pour des raisons évidentes d'efficacité numérique. C'est pourquoi une méthode de remaillage dynamique d'éléments coque vers des éléments solides est présentée et évaluée. Cette méthode permet d'obtenir des prédictions fiables de l'initiation de la rupture dans des tôles sans compromettre dramatiquement l'efficacité numérique obtenue grâce aux éléments coque. La seconde partie de ce travail s'intéresse aux micro-mécanismes responsables de la rupture ductile du matériau étudié. Une analyse micrographique du matériau soumis à différents niveaux de déformation permet d'identifier l'enchainement des mécanismes d'endommagement. Ces observations suggèrent que le mécanisme critique conduisant à la rupture est la localisation de la déformation plastique dans une bande de cisaillement à l'échelle du grain. Un model numérique reposant sur la déformation d'une cellule élémentaire 3D contenant une cavité est développé pour modéliser ce phénomène. Il est montré que le mécanisme de localisation à l'échelle micro de l'écoulement plastique dans une bande de cisaillement permet d'expliquer la dépendance de la ductilité à l'état de contrainte et au taux de déformation observée à l'échelle macro.
• Mechanical evolution of an altered limestone using 2D and 3D digital image correlation (DIC)
  
  • Zinsmeister L.
  • Dautriat J.
  • Dimanov A.
  • Raphanel J.
  • Bornert Michel
  , 2013, pp.16 p.. In the context of long term CO2 sequestration, we present an original laboratory workflow which allows a multi scale analysis of the effect of chemical alteration on both petrophysical and mechanical properties of a carbonate. The relationship between the mechanical behavior and the micro-structural evolutions is investigated using digital image correlation methods. For this purpose we imaged intact and altered samples during uniaxial and triaxial mechanical tests using optical microscopy, scanning electron microscopy (SEM) and 3D X-ray micro-tomography. The porosity increase induced by homogeneous alteration leads to lower elastic moduli and critical stress at sample failure. Furthermore, at similar confining pressures we observed a transition from brittle to ductile failure mechanisms with the alteration level. These observations are verified by digital image correlation. Altered samples indicate early strain localization which was not observed in the intact ones. These early localization events induce more compaction at the macroscopic scale and tend to initiate early fracturing.
• Surface-based electrophysiology modeling and assessment of physiological simulations in atria
  
  • Collin Annabelle
  • Gerbeau Jean-Frédéric
  • Hocini Mélèze
  • Haïssaguerre Michel
  • Chapelle Dominique
  , 2013, 7945, pp.352-359. The objective of this paper is to assess a previously-proposed surface-based electrophysiology model with detailed atrial simulations. This model - derived and substantiated by mathematical arguments - is specifically designed to address thin structures such as atria, and to take into account strong anisotropy effects related to fiber directions with possibly rapid variations across the wall thickness. The simulation results are in excellent adequacy with previous studies, and confirm the importance of anisotropy effects and variations thereof. Furthermore, this surface-based model provides dramatic computational benefits over 3D models with preserved accuracy. (10.1007/978-3-642-38899-6_42)
  DOI : 10.1007/978-3-642-38899-6_42
• Dimensional Reduction of Cardiac Models for Effective Validation and Calibration
  
  • Caruel Matthieu
  • Chabiniok Radomir
  • Moireau Philippe
  • Lecarpentier Yves
  • Chapelle Dominique
  , 2013, 7945, pp.259-267. Complex 3D beating heart models are now available, but their complexity makes calibration and validation very difficult tasks. We thus propose a systematic approach of deriving simplified reduced- dimensional models, in "0D" - typically, to represent a cardiac cavity, or several coupled cavities - and in "1D" - to model elongated structures such as fibers or myocytes. As illustrations of our approach, we demon- strate model validation based on experiments performed with papillary muscles, and calibration using patient-specific pressure-volume loops.
• Improving Efficiency of Data Assimilation Procedure for a Biomechanical Heart Model by Representing Surfaces as Currents
  
  • Imperiale Alexandre
  • Routier Alexandre
  • Durrleman Stanley
  • Moireau Philippe
  , 2013, 7945, pp.342-351. We adapt the formalism of currents to compare data surfaces and surfaces of a mechanical model and we use this discrepancy measure to feed a data assimilation procedure. We apply our methodology to perform parameter estimation in a biomechanical model of the heart using synthetic observations of the endo- and epicardium surfaces of an infarcted left ventricle. We compare this formalism with a more classical signed distance operator between surfaces and we numerically show that we have improved the efficiency of our estimation justifying the use of state-of-the-art computational geometry formalism in the data assimilation measurements processing. (10.1007/978-3-642-38899-6_41)
  DOI : 10.1007/978-3-642-38899-6_41
• Variational models for an elastic structure containing a periodic layer of fibers whose cross-section has a size of the same order of the period
  
  • Geymonat Giuseppe
  , 2013.
• Effects of a rapid depressurization in a salt cavern
  
  • Berest Pierre
  • Djizanne Hippolyte
  • Brouard Benoit
  • Hévin Grégoire
  , 2013, pp.653-658. Rapid gas depressurization leads to gas cooling followed by slow gas warming when the cavern is kept idle. Gas temperature drop depends upon withdrawal rate and cavern size. Thermal tensile stresses, resulting from gas cooling, may generate frac-tures at the wall and roof of a salt cavern. These fractures are perpendicular to the cavern wall; in most cases their depth of penetration is small. The distance between two parallel fractures becomes larger when fractures penetrate deeper in the rock mass, as some fractures stop growing. These conclusions can be supported by numerical computations based on fracture mechanics. Salt slabs are created. These slabs remain strongly bounded to the rock mass and it is believed that in many cases their weight is not large enough to allow them to break off the cavern wall. However, depth of penetration of the fractures must be computed to prove that they cannot be a concern from the point of view of cavern tightness.
• Polarization-resolved SHG microscopy of rat-tail tendon with controlled mechanical strain
  
  • Gusachenko Ivan
  • Goulam Houssen Yannick
  • Tran V.
  • Allain Jean-Marc
  • Schanne-Klein Marie-Claire
  , 2013, 8797, pp.SHG/THG/CARS/SRS I. (10.1117/12.2032627)
  DOI : 10.1117/12.2032627
• Gradient Theory: Constitutive Models and Fatigue Criteria; Application in Micromechanics
  
  • Luu D.H.
  , 2013. In the present thesis, two new classes of phenomenological models in the framework of the continuum thermodynamics and gradient theory are proposed. The first one is standard gradient constitutive model used to deal with the mechanical problems at micro-scale, and the other concerns gradient fatigue criteria for the problems at small scale. Using these, some common effects which are not captured yet in the classical mechanics but become significant at sufficiently small scales, are taken into account. For each class, the size and gradient effects which are the two effects most commonly discussed and very confused between each other in the literature, are clearly distinct and demonstrated to be integrated into the later via gradient terms. The thesis contains two principal contents presented in the part A and part B, respectively corresponding to the two new model classes. The following are their summary: Part A- Standard Gradient Constitutive Models: Application in Micro-Mechanics. A formulation of Standard Gradient Plasticity Models, based on an abundant researches on strain gradient plasticity (SPG) theory in the literature such as the ones of Q.S. Nguyen (2000, 2005, 2011 and 2012), is proposed and numerically implemented. The models are based on a global approach in the framework of continuum thermodynamics and generalized standard materials where the standard gradients of the internal parameters in the set of state variables are introduced. The governing equations for a solid are derived from an extended version of the virtual work equation (Frémond, 1985 or Gurtin, 1996). These equations can also be derived from the formalism of energy and dissipation potentials and appear as a generalized Biot equation for the solid. The gradient formulation established in such way is considered a higher-order extension of the local plasticity theory, with the introduction of the material characteristic length scale and the insulation boundary condition proposed by Polizzotto. The presence of strain gradient leads to a Laplacian equation and to non-standard boundary value problem with partial differential equations of higher order. A computational method, at the global level, based on diffusion like-problem spirit is used. Illustrations are given and applied to some typical problems in micro-mechanics to reproduce the well-known mechanical phenomenon, the effect "smaller is stronger". A good agreement between numerical results and reference counterparts is found; mesh-independence of numerical results is observed. Part B- Gradient Fatigue Criteria at Small Scale. A reformulation of gradient fatigue criteria is proposed in the context of multiaxial high-cycle fatigue (HCF) of metallic materials, initiated by Papadopoulos 1996. The notable dependence of fatigue limit on some common factors concerning the material specimen size is analysed and modeled. These factors, which are not taken into account before in classical fatigue criteria but become significant at sufficiently small scales, are included in the new formulation. Among such factors, three ones intimately related to each other, the pure size (smaller is stronger), stress gradient (higher gradient is higher resistance) and loading (i.e. loading mode) effects, are here investigated. An effort has been made to roughly integrate all these effects into only one through gradient terms. According to that, a new class of fatigue criteria with stress gradient terms introduced not only in the normal stress but also in the shear stress parts, are formulated. Such a formulation allows to capture all the pure size (if important) and stress gradient (if any) effects, as well as to cover a wide range of loading effect (traction, bending and shearing, for instance). Due to such a property, these new criteria are naturally generalized to multiaxial loadings to be a new version of stress gradient dependent multiaxial fatigue criteria. Application to some classical fatigue criteria such Crossland and Dang Van is provided as illustrations. As shown, classical fatigue criteria as well as the one of Papadopoulos 1996, are considered special cases of the new respective criteria. An overview for the whole thesis is put in this Summary, and an overview for each model class is found in the Chapter 1 where a general introduction of the thesis is given. Their corresponding detail are presented in the Chapters 2-4 (for part A) and Chapters 5-6 (for part B). The last chapter, Chapter 7, is dedicated to general conclusions and perspectives.
• Muscle as a Metamaterial Operating Near a Critical Point
  
  • Caruel Matthieu
  • Allain Jean-Marc
  • Truskinovsky Lev
  Physical Review Letters, American Physical Society, 2013, 110, pp.248103. The passive mechanical response of skeletal muscles at fast time scales is dominated by long range interactions inducing cooperative behavior without breaking the detailed balance. This leads to such unusual ''material properties'' as negative equilibrium stiffness and different behavior in force and displacement controlled loading conditions. Our fitting of experimental data suggests that ''muscle material'' is finely tuned to perform close to a critical point which explains large fluctuations observed in muscles close to the stall force. (10.1103/PhysRevLett.110.248103)
  DOI : 10.1103/PhysRevLett.110.248103
• Structural effects in dynamic testing of brittle materials
  
  • Gary Gérard
  , 2013. Dynamic testing of brittle materials obviously involves the specificities of dynamics and of the special kind of behaviour that describes brittle material. The interaction of both aspects is much more important than for materials like metals which exhibit a plastic behaviour. This interaction is described in the present paper, with a special focus on the Split Hopkinson bar technique commonly used in these fields.
• Asymptotic analysis of small defects near a singular point in anti-plane elasticity. Application to the nucleation of a crack at a notch
  
  • Dang Thi Bach Tuyet
  • Halpern Laurence
  • Marigo Jean-Jacques
  Mathematics and Mechanics of Complex Systems, International Research Center for Mathematics & Mechanics of Complex Systems (M&MoCS),University of L’Aquila in Italy, 2013, pp.sous presse. We use matching asymptotic expansions to treat the anti-plane elastic problem associated with a small defect located at the tip of a notch. In a first part, we develop the asymptotic method for any type of defect and present the sequential procedure which allows us to calculate the different terms of the inner and outer expansions at any order. That requires in particular to separate in each term its singular part from its regular part. In a second part, the asymptotic method is applied to the case of a crack of variable length located at the tip of a given notch. We show that the first two non trivial terms of the expansion of the energy release rate are sufficient to well approximate the dependence of the energy release rate on the crack length in the range of values of the length which are sufficient to treat the problem of nucleation. This problem is considered in the last part where we compare the nucleation and the propagation of a crack predicted by two different models: the classical Griffith law and the Francfort-Marigo law based on an energy minimization principle. Several numerical results illustrate the interest of the method.
• Microsphere model for strain-induced crystallization in rubber
  
  • Guilie Joachim
  • Lê Thien-Nga
  • Le Tallec Patrick
  , 2013, pp.p 467-472.
• A non-smooth simulation of the dynamics of the grand piano action
  
  • Thorin Anders
  • Boutillon Xavier
  • Merlhiot Xavier
  • Lozada José
  , 2013. Two models of the grand piano key mechanism are presented: a single-degree-of-freedom model and a model based on 6 rotating bodies, 13 contact zones with nonlinear springs, 3 of them (hammer-jack, jack-escapement button, hammer-check) being also subject to Coulomb friction. The latter model introduces discontinuities on the velocities. The problems raised by the usual regular-dynamics formulation are discussed and a non-smooth dynamics approach is proposed. Based on the comparison between experimental and simulation results, it is discussed whether the simulation should be driven by the force exerted by the pianist or by the displacement of the key.
• Vibration model of piano soundboards
  
  • Boutillon Xavier
  • Ege Kerem
  , 2013. Modal observations of a piano soundboard are compared with results predicted by a model consisting of weakly coupled homogeneous sub-structures. The model is entirely determined by the coarse geometry of the soundboard (main plate, ribs, bridges, cut-off corners) and by the elastic parameters of the wood species. It can also be used to predict the point-mobility at the bridge (where strings are attached) or far from it. The agreement between observations and model predictions is excellent, both in the low- and high-frequency regimes (respectively below and above approximately 1 kHz). Applications include a comparison between the characteristics of different pianos as well as the influence of the wood properties on the point-mobility. Some consequences in terms of acoustical radiation will also be presented.
• Infrared thermography: a powerful tool to characterize the thermomechanical and fatigue properties of short glass fiber reinforced thermoplastics structural samples
  
  • Le Saux V.
  • Marco Yann
  • Launay Antoine
  • Jegou Loïc
  • Calloch Sylvain
  , 2013, pp.XXX.
• Quantitative investigation of grain boundary sliding in halite rock by SEM in situ testing and full field strains measurements
  
  • Gaye Ababacar
  • Bourcier Mathieu
  • Heripre Eva
  • Bornert Michel
  • Dimanov Alexandre
  • Raphanel Jean
  • Sab Karam
  , 2013, pp.5 p.. An experimental investigation of the deformation mechanisms acting in halite at the scale of its polycrystalline microstructure is presented. Uniaxial compression tests on centimetric samples are performed inside the chamber of a scanning electron microscope and the obtained high definition images are processed by digital image correlation (DIC) routines. A special marking procedure provides an appropriate contrast at microscale. Standard DIC routines qualitatively demonstrate the coexistence of two deformation mechanisms: crystal slip plasticity and grain boundary sliding. A specific post-processing of the DIC-evaluated displacement fields provides a first quantification of the relative contribution of these mechanisms to overall strain and a dependence with grain size can be demonstrated. A modified DIC formulation able to separate intra-grain deformation from interfacial gliding is also proposed for a better quantification and preliminary results are presented. Such data will be of primary interest for the construction of physically-based multiscale models of the mechanical properties of halite, which might be used for security assessment of deep caverns in salt-rock.
• Micromechanics of argillaceous rocks investigated by means of in situ hydromechanical testing in an environmental scanning electron microscope
  
  • Wang Linlin
  • Bornert Michel
  • Heripre Eva
  • Caldemaison Daniel
  • Chanchole Serge
  , 2013.
• Nonlinear Donati compatibility conditions for the nonlinear Kirchhoff -von K arm an-Love plate theory
  
  • Ciarlet Philippe G.
  • Geymonat Giuseppe
  • Krasucki Francoise
  Comptes rendus hebdomadaires des séances de l'Académie des sciences, Gauthier-Villars, 2013, 351, pp.405-409. Linear Donati compatibility conditions guarantee that the components of symmetric tensor fields are those of linearized change of metric or linearized change of curvature tensor fields associated with the displacement vector field arising in a linearly elastic structure when it is subjected to applied forces. These compatibility conditions take the form of variational equations with divergence-free tensor fields as test-functions, by contrast with Saint-Venant compatibility conditions, which take the form of systems of partial differential equations. In this paper, we identify and justify nonlinear Donati compatibility conditions that apply to a nonlinearly elastic plate modeled by the Kirchhoff-von K'arm'an-Love theory. (10.1016/j.crma.2013.05.012)
  DOI : 10.1016/j.crma.2013.05.012
• 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.
• Standard gradient plasticity: formulation and numerical integration
  
  • Luu Duy-Hao
  • Maitournam Habibou
  • Nguyen Son
  , 2013. The paper is devoted to the numerical implementation of a strain gradient plasticity model proposed by Q.S Nguyen. The model combining isotropic and kinematic hardening uses gradient of accumulated plastic strain to reproduce micro-mechanical features related to size effect. Its formulation is presented within the general framework of the classical continuum thermodynamics. Its numerical integration meets difficulties by the presence of strain gradients in the local theory formulation, which leads to a Laplacian equation solved at global level and to boundary value problems governed by partial differential equations of higher order with non-standard boundary conditions. A methodology of a diffusion-like problem is used to overcome this difficulty. This work is numerically solved via UMATs constructed in common available FE codes (e.g. Cast3M).
• Cyclic behavior of elasto-plastic porous materials subjected to triaxial loading conditions
  
  • Mbiakop Armel
  • Carpiuc Andreea
  • Constantinescu Andrei
  • Danas Kostas
  , 2013. This work proposes an analysis of the effect of cyclic loading of elasto-plastic porous materials upon the microstructure evolution and possible failure of the material due to low cycle fatigue. In order to investigate this effect, periodic FEM unit-cell calculations are carried out subjected to various stress triaxialities and Lode angles. The present results indicate that the absolute value of the stress triaxiality as well as of the value of the Lode angle are critical for the microstructure evolution and the subsequent material response. In addition, even though the macroscopic applied strains are relatively small, i.e., in the order of a few per cent, the local strains obtained near the pore surface can increase significantly (even more than 100%) due to significant localization of the deformation. This in turn leads to a critical evolution of the pore shape and as a consequence to porosity evolution.