Publications

2004

• Fatigue crack growth under non-proportional mixed-mode loading in ferritic-pearlitic steel
  
  • Doquet Véronique
  • Pommier Sylvie
  Fatigue and Fracture of Engineering Materials and Structures, Wiley-Blackwell, 2004, 27 (11), pp.1051-1060. Mode II fatigue crack growth tests as well as tests in sequential mode I and then mode II were performed on ferritic‐pearlitic steel. For ΔKII ranging from 7 to 43MPa√m, bifurcation occurs after 12–450μm of coplanar growth at a decreasing speed. By contrast, hundreds of micrometres of constant speed coplanar growth were obtained under sequential mode I and then mode II loading, for ΔKII=20MPA√m and ΔKI ranging from 0.25 to 1.0 ΔKII. The crack growth rate is a simple sum of the contributions of each mode for ΔKI= 0.25 ΔKII but above this value a synergetic effect is found. The mechanism of this fast‐propagation mode is discussed in the light of strain range maps ahead of the crack tip obtained by digital SEM image correlation and elastic–plastic finite element calculations. The stability of the crack path according to the maximum growth rate criterion is demonstrated. (10.1111/j.1460-2695.2004.00817.x)
  DOI : 10.1111/j.1460-2695.2004.00817.x
• Nonlinear affine extension of the three-phase sphere model
  
  • Chabert Emmanuelle
  • Bornert Michel
  • Zaoui André
  , 2004. To model the nonlinear behaviour of particulate composites, the classical procedure of transforming, at a given strain, a nonlinear problem into a linear one has been used. The chosen linearisation method is the recently proposed affine formulation [1,2] which has been coupled to the three phase self-consistent estimate [3] of the linearised overall properties, in the case of uniaxial loading. This modelling has been applied to two-phase composites with nonlinear elastic behaviours described by power-law stress-strain relationships, but the same developments are still valid for viscous materials.
• Contribution à l'étude du changement de phase liquide-vapeur dans des capillaires micrométriques en vue des applications aux étanchéités statiques
  
  • Jolly Pascal
  , 2004. Ce travail a pour objet la compréhension de la phénoménologie du changement de phase liquide-vapeur lors de l'écoulement d'un fluide dans des chemins de fuite micrométriques, résultants du contact imparfait entre deux pièces métalliques du fait de la rugosité des parois. Le but est de déterminer l'influence du changement d'état du fluide sur la valeur du débit de fuite par rapport à un écoulement monophasique. Le chemin de fuite est assimilé à un capillaire micrométrique de section circulaire, aux extrémités duquel les conditions de pression correspondent à l'état liquide en entrée et à l'état vapeur en sortie. L'étude se limite aux situations où le changement de phase est obtenu par une chute de la pression locale le long du capillaire, sans apport de chaleur complémentaire à la paroi. L'ensemble des équations phasiques et interfaciales sont rendues sans dimension afin d'identifier, par une analyse phénoménologique, les mécanismes prépondérants lors de l'ébullition du R134a en espace confiné. Il est montré que le changement de phase intervient par nucléation hétérogène et que la croissance des bulles de vapeur ainsi formées est contrôlée par les phénomènes thermiques. Un dispositif expérimental est conçu pour observer le changement de phase dans des capillaires en verre, dont le diamètre intérieur est compris dans une gamme de 20 à 100 $\mu m$. Un protocole d'essais très strict est suivi au cours des expériences pour s'assurer que les conditions d'équilibre sont atteintes. L'évolution de la taille des inclusions gazeuses, quand elles se produisent, est relevée à l'aide d'une caméra rapide ou d'une webcam. A partir de ces visualisations, on peut estimer l'effet du changement de phase sur le débit de fuite. Selon l'historique de variation de la pression en aval du capillaire, il existe une situation où aucune bulle de vapeur ne se forme, le liquide supportant la surchauffe jusqu'à la sortie.
• From Galileo to Convexity: some key ideas in structural mechanics
  
  • Salençon Jean
  , 2004. The main topic treated in the First Day and the Second Day of Galileo’s Dialogues is the resistance that solids offer to fracture with special consideration to prisms and cylinders submitted to axial tensile loading or to “transverse”, i. e. bending, forces. Although no consideration is given to deformation of the solid before fracture one may say that Galileo implicitly introduces the concept of a Continuum within which coherence forces do act in order to maintain the filaments, fibres or any other constituent particles together. Thus, he opens the way to the concept of stress, which was settled explicitly some 200 years later. Having recognised that coherence forces and gravity forces in a solid are not related in the same way to its geometric scale, he performs what can be considered as the first striking example of dimensional analysis with application to similarity. In its celebrated analysis of the resistance of a cantilever beam submitted to bending, Galileo gives a first attempt to deriving the resistance of a whole solid submitted to some kind of loading from the resistance of its constituent material determined from another test. Together with Coulomb’s celebrated Essay these are two milestones of the Theory of yield design, the fundamental root of Ultimate Limit State Design, which is presently introduced in international codes for civil engineering
• Modélisation du gonflement des argiles et de ses effets sur les ouvrages de stockage souterrain.
  
  • Gaombalet Jérôme
  , 2004. Le travail qui est présenté dans ce document a été réalisé au laboratoire G.3S (Groupement pour l'étude des Structures Souterraines de Stockage) de l'Ecole Polytechnique, à Palaiseau. Le G.3S est un G.I.P. (Groupement d'Intérêt Public) fonctionnant grâce à la réalisation de contrats de recherches industrielles. Ces recherches, à caractère expérimental ou de modélisation numérique, portent pour la plupart sur les roches intéressant le stockage souterrain, de déchets radioactifs en particulier. L'accent est mis sur les différents couplages thermohydromécaniques (THM) susceptibles d'intervenir, au champ proche comme au champ lointain.
• Optimal control and inverse problem in non linear mechanics
  
  • Stolz Claude
  , 2004.
• The challenge of defining upper bounds on earthquake ground motions
  
  • Bommer Julian J
  • Abrahamson Norman A
  • Strasser Fleur O
  • Pecker Alain
  • Bard Pierre-Yves
  • Bungum Hilmar
  • Cotton Fabrice
  • Fäh Donat
  • Sabetta Fabio
  • Scherbaum Frank
  • Studer Jost
  Seismological Research Letters, Seismological Society of America, 2004, 75, pp.82-95. Recent studies to assess very long-term seismic hazard in the United States and in Europe have brought the issue of upper limits on earthquake ground motions into the arena of problems requiring attention from the engineering seismological community. Few engineering projects are considered sufficiently critical to warrant the use of annual frequencies of exceedance so low that ground-motion estimates may become unphysical if limiting factors are not considered, but for nuclear waste repositories, for example, the issue is of great importance. The definition of upper bounds on earthquake ground motions also presents an exciting challenge for researchers in the area of seismic hazard assessment. This paper looks briefly at historical work on maximum values of ground-motion amplitudes before illustrating why this is an important issue for hazard assessments at very long return periods. The paper then discusses the factors that control the extreme values of motion, both in terms of generating higher amplitude bedrock motions and of limiting the values of motion at the ground surface. Possible channels of research that could be explored in the quest to define maximum possible ground motions are also discussed. (10.1785/gssrl.75.1.82)
  DOI : 10.1785/gssrl.75.1.82
• Tailoring bulk and surface grafting of poly(acrylic acid) in electron-irradiated PVDF
  
  • Clochard Marie-Claude
  • Bègue J
  • Lafon A
  • Caldemaison D
  • Bittencourt C
  • Pireaux J.-J
  • Betz N
  Polymer, Elsevier, 2004, 45, pp.8683. Endowing conventional hydrophobic poly(vinylidene fluoride) (PVDF) films with hydrophilic properties was conducted using electron beam irradiation. Grafting of acrylic acid (AA) in/onto pre-irradiated PVDF films was investigated. Reaction parameters, monomer concentration and inhibitor concentration were examined. Radiation grafted films (PVDF-g-PAA) were synthesized with various grafting yields ranging from 12 to 130 wt % in presence of Mohr's salt (25 wt %). Below 80 wt % of monomer concentration, the degree of swelling was found to increase with the grafting yield. The PAA was arranged randomly in all PVDF matrix (grafting through). Above 80 wt % of monomer concentration, the PAA was grafted only onto the surface of PVDF films leading to a highly dense layer of PAA. Grafting through or surface grafting processes were achieved by varying the water fraction in the initial monomer solution. Water molecule acts not only as a carrier for the monomer but also as a plasticizer expanding the film in the three dimensions. Evidences of grafting through and surface grafting were produced using FTIR in ATR mode, SEM coupled to X-ray detection and XPS. An accurate quantification of AA units was possible up to the micromole via a Cu 2C –EDTA complex analyzed by UV–vis spectroscopy. q (10.1016/j.polymer.2004.10.052)
  DOI : 10.1016/j.polymer.2004.10.052
• Experimental study of the influence of the degree of saturation on physical and mechanical properties in Tournemire shale (France)
  
  • Valès Frédéric
  • Nguyen-Minh Duc
  • Gharbi Hakim
  • Rejeb Amel
  Applied Clay Science, Elsevier, 2004, 26 (1-4), pp.197-207. In addition to direct mechanical perturbations, an excavation influences rock conditions (mechanical, hydraulic and chemical properties). The internal fluids could be drastically modified and, in particular, the presence of water in the rock with regard to hydration and desiccation. The aim of the present study is to investigate the influence between the degree of saturation and the physical/mechanical properties for Tournemire shale rock. Anisotropy effects are also studied to identify hydromechanical behaviour. The different degrees of saturation are imposed by controlled suctions with continuous measurement of physical parameters such as weight and deformations. The volume variations (swelling or shrinkage behaviour) would result principally from the opening or closing of the inter-layers space. Uniaxial and triaxial compressive tests are carried out in order to attempt to establish a relationship between different mechanical parameters (elastic and failure data) and the sample saturation. The mechanical behaviour is sensitive to the saturation state of the shale with an important part of the stratification and its relative orientation to the mechanical stress. (10.1016/j.clay.2003.12.032)
  DOI : 10.1016/j.clay.2003.12.032
• Second-order estimates for the macroscopic response and loss of ellipticity in porous rubbers at large deformations
  
  • Lopez-Pamies Oscar
  • Ponte Castañeda Pedro
  Journal of Elasticity, Springer Verlag, 2004, 76 (3), pp.247-287. This work presents the application of a recently proposed “second-order” homogenization method (Ponte Castañeda, 2002) to generate estimates for effective behavior and loss of ellipticity in hyperelastic porous materials with random microstructures that are subjected to finite deformations. The main concept behind the method is the introduction of an optimally selected “linear thermoelastic comparison composite”, which can then be used to convert available linear homogenization estimates into new estimates for the nonlinear hyperelastic composite. In this paper, explicit results are provided for the case where the matrix is taken to be isotropic and strongly elliptic. In spite of the strong ellipticity of the matrix phase, the homogenized “second-order” estimates for the overall behavior are found to lose ellipticity at sufficiently large compressive deformations corresponding to the possible development of shear band-type instabilities (Abeyaratne and Triantafyllidis, 1984). The reasons for this result have been linked to the evolution of the microstructure, which, under appropriate loading conditions, can induce geometric softening leading to overall loss of ellipticity. Furthermore, the “second-order” homogenization method has the merit that it recovers the exact evolution of the porosity under a finite-deformation history in the limit of incompressible behavior for the matrix. (10.1007/s10659-005-1405-z)
  DOI : 10.1007/s10659-005-1405-z
• Topological sensitivity for 3D elastic and acoustic inverse scattering
  
  • Bonnet Marc
  , 2004. (10.1016/j.cma.2005.10.026)
  DOI : 10.1016/j.cma.2005.10.026
• Elastodynamic rendering of internal cavities by way of topological derivative
  
  • Bonnet Marc
  • Guzina Bojan B
  , 2004.
• Identification de loi de comportement cristallines à partir du couplage EBSD/Microextensométrie/Eléments Finis. Application au zirconium grade 702
  
  • Dexet Marie
  • Crépin Jérôme
  • Gélébart Lionel
  • Zaoui André
  , 2004.
• Topological sensitivity for 3D elastic and acoustic inverse scattering
  
  • Bonnet Marc
  , 2004. (10.1016/j.cma.2005.10.026)
  DOI : 10.1016/j.cma.2005.10.026
• Sandstone compaction by intergranular pressure solution
  
  • Lehner F. K.
  • Leroy Y. M.
  , 2004, pp.115-168. This chapter discusses sandstone compaction by intergranular pressure solution and presents the theoretical means for exploring problems of stress-sensitive dissolution and coupled macroscopic deformation and transport. The simple one-dimensional compaction model discussed in this chapter represents only a first exploratory study of the behavior of the proposed model. Despite carrying out a numerical study for only one-layer thickness and a single set of initial and boundary conditions, the results obtained for this case have yielded some basic insights into the behavior of the compaction model that can also point the way for future studies. When precipitation was inhibited, the exceedingly slow diffusive transport over 5,000 m of layer thickness was found to lead to the build-up of high (possibly unrealistic) supersaturations, approximately 1.5 times the equilibrium concentration, which slowed down intergranular dissolution to extremely low rates. However, because this low-rate limit in compaction behavior is likely to be attained only in the absence of any significant advective influx of undersaturated fluid through the base of the layer, the role of the prevailing hydrological regime in compacting sedimentary layers is immediately apparent. This observation suggests that in a sedimentary column that is open only at its top, macroscopic advection will be activated only if there exist local sinks—the free faces—on the grain scale, where the material at a nearby grain boundary can be deposited. (10.1016/S0074-6142(03)80019-0)
  DOI : 10.1016/S0074-6142(03)80019-0
• Contributions of internal hydrogen and room-temperature creep to the abnormal fatigue cracking of Ti6246 at high Kmax
  
  • Mignot Frédéric
  • Doquet Véronique
  • Sarrazin-Baudoux Christine
  Materials Science and Engineering: A, Elsevier, 2004, 380 (1-2), pp.308-319. This study aims at explaining the absence of a threshold for crack propagation in an α/β titanium alloy during cyclic tests performed with constant Kmax and increasing Kmin, if Kmax is higher than 60–70% of KIc. Tensile, creep as well as fatigue crack growth tests are performed on specimens with various hydrogen content. SIMS analyses of hydrogen content around the tip of a crack developed in the abnormal regime are made. Solute hydrogen is shown to segregate at the crack tip and to enhance room-temperature creep, strain localisation and decohesion along α/β interfaces. (10.1016/j.msea.2004.04.006)
  DOI : 10.1016/j.msea.2004.04.006
• Experimental and numerical rolling contact fatigue study on the 32CrMoV13 steel
  
  • Coelho Luís
  • Mourão Dias Antonio Angelo
  • Lieurade Henri-Paul
  • Maitournam Habibou
  Fatigue and Fracture of Engineering Materials and Structures, Wiley-Blackwell, 2004, 27, pp.811-823. The aim of this work is to study pure rolling contact fatigue in 32CrMoV13 quenching and tempering steel. The study involves both experimental and numerical work. The influence of the roughness and the residual stresses on the mechanisms and zones of cracking were studied. The results show a rapid reduction in roughness during the first minute of test but even so there will be specimen deterioration. The residual stress profile after rolling contact tests have high compression values in the surface and at a depth of approximately 240 μm, which is related with the Hertzian maximal shear stress. The numerical simulation of the Hertzian loading was used both to determine the elastic shakedown of the material and to apply a high‐cycle multiaxial fatigue criterion. The three‐dimensional finite element analysis used in the numerical calculation includes elastic‐linear kinematic hardening plastic material and allows the introduction of an initial residual stress state. Taking into account the elastoplastic load induced by the Hertz pressure, low‐cycle fatigue tests were used to characterize the mechanical properties of the material. In order to validate the numerical simulation, the results of the calculation after elastic shakedown were compared with the values measured by X‐ray diffraction after rolling contact tests. The results showed a reasonable agreement between calculated and measured stresses. The Dang Van high‐cycle multiaxial fatigue criterion showed a good relationship with the experimental findings. (10.1111/j.1460-2695.2004.00797.x)
  DOI : 10.1111/j.1460-2695.2004.00797.x
• Mesure tridimensionnelle des champs de déformation par corrélation d'images microtomographiques
  
  • Bornert Michel
  • Doumalin Pascal
  • Maire Eric
  , 2004, pp.33-40. On présente une extension de la technique de mesure de champs cinématiques par corrélation aux images tridimensionnelles obtenues par microtomographie sous rayonnement synchrotron. Les matériaux analysés, élaborés par métallurgie des poudres, sont des alliages d’aluminium, éventuellement renforcés par des particules sphériques de zircone-silice, dont le diamètre est de quelques centaines de micromètres. Le contraste tomographique nécessaire à l’analyse d’image est fourni par des grains de cuivre d’un diamètre de 5 à 10µm, plus dense que l’aluminium, introduits dans la matrice à raison de 5%, de telle sorte que le « mouchetis volumique » ainsi obtenu autorise une mesure de déplacement tous les 40µm avec des domaines de corrélation typiques de 203 voxels, la résolution des images étant d’environ 2µm. Un dispositif de traction transparents aux rayons X permet de solliciter des échantillons de forme cylindrique dont la section varie de 1 à 4 mm2. Des essais de validation avec des mouvements de translation sans déformation révèlent une précision potentielle de mesure de l’ordre de 0,02 voxels, les erreurs maximales coïncidant avec les artefacts de reconstruction tomographique. Les champs mesurés sur des échantillons entaillés de matrice non renforcée, sollicités en traction sont comparés aux mesures obtenues par microextensométrie de surface sous microscope électronique à balayage.
• Extension non linéaire du modèle des ''3 phases'' par la méthode affine
  
  • Chabert E.
  • Bornert Michel
  • Zaoui A.
  , 2004. No abstract provided
• Filler-filler interactions and viscoelastic behavior of polymer nanocomposites
  
  • Chabert Emmanuelle
  • Bornert Michel
  • Bourgeat-Lami Elodie
  • Cavaillé Jean-Yves
  • Dendievel Remy
  • Gauthier Catherine
  • Putaux Jean-Luc
  • Zaoui André
  Materials Science and Engineering: A, Elsevier, 2004, 381 (1-2), pp.320-330. This work presents the main results obtained within a project on mechanical properties of polymer based nanocomposites. The specific point was how to analyze and model the filler–filler interactions in the description of the viscoelastic behavior of these materials. This paper aims at presenting the general strategy used by the different partners to address this question, together with original experimental results and micro-mechanical modeling. Different nanocomposite materials were fabricated using the latex route, leading to random dispersions of rigid submicronic particles (PS = polystyrene, silica) in a flexible polybutylacrylate matrix at various volume fractions. In addition, encapsulated silica particles in a styrene–acrylate copolymer were produced, leading, after film formation, to a limited number of contacts between silica fillers. The processing route of these encapsulated particles was optimized and the resulting morphology was analyzed by TEM experiments. In the case of random mixtures, a strong effect of reinforcement appears in the rubbery field of the soft phase when the filler content is above a critical fraction (percolation threshold). The reinforcement in the rubbery plateau can be still exacerbated in the case of the PS particles if the material undergoes a heat treatment above the main relaxation of the PS phase. These experimental results illustrate the difference between geometrical percolation (when particles are just in contact) and mechanical percolation (with strong interactions between the fillers). The comparison of the results for PS and silica fillers shows once more that the strength of the interactions plays an important role. To account for the whole set of experimental data, two ways of modeling were explored: (i) homogenization methods based on generalized self-consistent schemes and (ii) a discrete model of spheres assembly which explicitly describes the ability of the contacts to transmit efforts. (10.1016/j.msea.2004.04.064)
  DOI : 10.1016/j.msea.2004.04.064
• Topological derivative applied to cavity identification from elastodynamic surface measurements
  
  • Bonnet Marc
  • Guzina Bojan B
  Revue Européenne des Éléments Finis, HERMÈS / LAVOISIER, 2004, 13, pp.425-436. This article is concerned with the use of topological derivative as a tool for preliminary elastic-wave probing of bounded or unbounded solids for buried objects. A formulation for computing the topological derivative field, based on an adjoint solution, is presented. A set of numerical results is included to illustrate the utility of topological derivative for outlining the cavity location and size prior to doing an actual inversion of measurements. The results presented here were obtained from a BIE solution, but the proposed methodology is applicable to other computational platforms such as the finite element method. (10.3166/reef.13.425-436)
  DOI : 10.3166/reef.13.425-436
• Comportement dynamique du béton. Aspects expérimentaux
  
  • Gary G.
  • Toutlemonde F.
  , 2004.
• Sounding of finite solid bodies by way of topological derivative
  
  • Bonnet Marc
  • Guzina B. B.
  Int. J. Num. Meth. in Eng., 2004, 61, pp.2344-2373. This paper is concerned with an application of the concept of topological derivative to elastic-wave imaging of finite solid bodies containing cavities. Building on the approach originally proposed in the (elastostatic) theory of shape optimization, the topological derivative, which quantifies the sensitivity of a featured cost functional due to the creation of an infinitesimal hole in the cavity-free (reference) body, is used as a void indicator through an assembly of sampling points where it attains negative values. The computation of topological derivative is shown to involve an elastodynamic solution to a set of supplementary boundary-value problems for the reference body, which are here formulated as boundary integral equations. For a comprehensive treatment of the subject, formulas for topological sensitivity are obtained using three alternative methodologies, namely (i) direct differentiation approach, (ii) adjoint field method, and (iii) limiting form of the shape sensitivity analysis. The competing techniques are further shown to lead to distinct computational procedures. Methodologies (i) and (ii) are implemented within a BEM-based platform and validated against an analytical solution. A set of numerical results is included to illustrate the utility of topological derivative for 3D elastic-wave sounding of solid bodies; an approach that may perform best when used as a pre-conditioning tool for more accurate, gradient-based imaging algorithms. Despite the fact that the formulation and results presented in this investigation are established on the basis of a boundary integral solution, the proposed methodology is readily applicable to other computational platforms such as the finite element and finite difference techniques. (10.1002/nme.1153)
  DOI : 10.1002/nme.1153
• Dissipation and fatigue damage
  
  • Charkaluk Eric
  • Constantinescu Andrei
  Materials Testing, 2004, 46, pp.524-530. The discussion of fatigue damage is generally separated in two domains : Low Cycle Fatigue (LCF) and High Cycle Fatigue (HCF). The transition zone concerns the case of limited endurance, while the unlimited endurance is generally assimilated with HCF. Fatigue failure is the result of complex microscopic phenomena wich occur under cyclic loading. However, the principal mechanism responsible for the crack initiation, common to all domains, is the spatial extension on inelastic strains (plastic or viscous) in the grains due to the motion of dislocations. The major difference between HCF and LCF regimes is that inelastic strains develop at the material's mesoscopic and macroscopic scles, respectively. As the underlying mechanics are the same, there should be no reason to have distinct criteria in HCF and LCF. The objective of this paper is to give further considerations based on dissipation towards a unified method to treat fatigue damage. (10.3139/120.100615)
  DOI : 10.3139/120.100615
• Structure and mechanical properties of AFS sandwiches studied by in situ compression tests in X-Ray microtomography
  
  • Salvo L.
  • Belestin P.
  • Maire Éric
  • Jacquesson Marie
  • Vecchionaci Claude
  • Boller Elodie
  • Bornert Michel
  • Doumalin Pascal
  Advanced Engineering Materials, Wiley, 2004, 6, pp.411-415. Al foam core / Al alloy skins sandwiches have potential for application in light weight structures. Recently, the foaming processes have improved and large, thick and 3D-shape panels can be produced using the precursor technology. The microstructure of an AFS sandwich is analysed in this paper at a microscale and a mesoscale using X-ray tomography and conventional SEM analysis. The main deformation mechanism of the core under compression is also studied thanks to in situ test. It is shown that the foam first present plastic buckling and then walls rupture. This is well correlated to the microstructure of the constitutive material of the core. (10.1002/adem.200405152)
  DOI : 10.1002/adem.200405152