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.
• Numerical identification of linear cracks in 2D elastodynamics using the instantaneous reciprocity gap
  
  • Bui Huy Duong
  • Constantinescu Andrei
  • Maigre Hubert
  Inverse Problems, IOP Publishing, 2004, 20, pp.993-1001. This paper considers the identification problem of a linear crack in a body of finite extension within the framework of linear two-dimensional elastodynamics. In a series of prior papers in electricity, elasticity or acoustics, it has been proved using the reciprocity gap that three different series of adjoint wave fields determine in closed-form solution the normal of the plane of the crack, the position of the plane and finally the complete crack extension. The work developed next within the framework of linear elastodynamics defines a novel instantaneous reciprocity gap as the instantaneous work done by the adjoint tractions on the crack opening displacement. This quantity is then used to identify linear cracks in a two-dimensional problem. It is shown using a numerical example that a unique family of planar shear waves permits the identification of the normal, position and a convex hull of a linear crack through simple interpretations of the instantaneous reciprocity gap. This method is more general in the sense that it applies to three-dimensional problems as well. (10.1088/0266-5611/20/4/001)
  DOI : 10.1088/0266-5611/20/4/001
• Fast multipole method applied to elastostatic BEM-FEM coupling
  
  • Margonari Massimiliano
  • Bonnet Marc
  , 2004, 83 (10-11), pp.700-717. BEM–FEM coupling is desirable for three-dimensional problems involving specific features such as (i) large or unbounded media with linear constitutive properties, (ii) cracks, (iii) critical parts of complex geometry requiring accurate stress analyses. However, for cases with a BEM discretization involving a large number NBEM of degrees of freedom, setting up the BEM contribution to the coupled problem using conventional techniques is an expensive task. Moreover, the fully-populated BEM block entails a storage requirement and a contribution to the solution time via usual direct solvers. To overcome these pitfalls, the BEM contribution is formulated using the fast multipole method (FMM) and the coupled equations are solved by means of an iterative GMRES solver. Both the storage requirements and the solution times are found to be close to O(NBEM). A preconditioner based on the sparse approximate inverse of the BEM block is shown to improve the convergence of the GMRES solver. Numerical examples involving NBEM = O(105 − 106) unknowns, run on a PC computer, are presented; they include the Eshelby inclusion (as a validation example), a many-inclusion configuration, and a dam structure. (10.1016/j.compstruc.2004.09.007)
  DOI : 10.1016/j.compstruc.2004.09.007
• Giens 2003
  
  • Bonnet Marc
  • Ben Dhia Hachmi
  • Allix Olivier
  , 2004.
• Propagation 3D de fissures dans l'inox 304L et simulations 2D d'évolutions de réseaux orthogonaux en fatigue biaxiale
  
  • Doquet V.
  • Kane A.
  , 2004. No abstract provided
• Mechanics of low-angle extensional shear zones at the brittle-ductile transition
  
  • Gueydan F.
  • Leroy Y.
  • Jolivet Laurent
  Journal of Geophysical Research, American Geophysical Union, 2004, 109 (B12407), pp.1-16. Low-angle midcrustal ductile shear zones and the related microseismic activity recorded below regions of active extension are seen here as two consequences of strain localization. The feldspar-to-mica reaction which occurs once feldspar grains are fractured is the destabilizing mechanism selected to explain the strain localization. The model problem considered to substantiate these claims is solved by numerical means and combines the simple shear due to the rigid gliding of the upper crust (at the velocity of V s ) and the stretch resulting from the extension of the whole crust (at the velocity V e ). The rheological model accounts for dislocation creep of quartz, feldspar, and mica, the feldspar-to-mica reaction, and its prerequisite, which is the feldspar fracturing detected by the Mohr-Coulomb criterion. The one-dimensional (1-D) solution, which constrains shear bands to be horizontal, shows the depth partitioning in deformation mode between the simple shear of the low-viscosity deep crust and the stretching of the highly viscous midcrust. Strain localization occurs during rapid increase of the shearing velocity V s , corresponding to low values of the velocity ratio V e /V s . The 2-D solution (for V e /V s = 10−3) reveals the development of a periodic system of extensional shear bands, dipping at 30° toward the shearing direction at a depth of 12 to 14 km. Shear bands are formed after less than half a million years at the base of the reaction zone defined by the region where feldspar-to-mica reaction is completed. Shear bands do not propagate to greater depths because the pressure prevents the feldspar from fracturing and thus the reaction to occur. The periodic system of shear bands defines a midcrustal flat weakened zone within which the equivalent shear stress is enhanced by at least a factor of three at the shear band tips. Brittle fracture could thus occur within the midcrustal flat weakened zone, explaining therefore the microseismicity monitored at these depths in regions of active extension. (10.1029/2003JB002806)
  DOI : 10.1029/2003JB002806
• Multiscale analysis of the transverse properties of Ti-based matrix composites reinforced by SiC fibres: from the grain scale to the macroscopic scale
  
  • Carrère Nicolas
  • Valle Roger
  • Bretheau Thierry
  • Chaboche Jean-Louis
  International Journal of Plasticity, Elsevier, 2004, 20, pp.783-810. It is well known that the presence of continuous fibres in SiC/Ti composites leads to a high mechanical anisotropy of the composite between the longitudinal and the two transverse directions. But it is also possible that the crystallographic texture of the matrix may lead to a non-negligible anisotropy of the mechanical properties of the composite. The crystallographic orientation of the matrix grains was determined using the Electron BackScattering Diffraction technique. A local texture of the matrix of the composite is thus evidenced. Finite Element calculations are used to determine the stress field in the matrix resulting from an applied transverse loading. The representative mechanical quantities thus determined are discussed in relation with the fundamental mechanisms of plastic deformation of the matrix. Finally, the crystallographic texture of the matrix of the composite is taken into account in the numerical modellings using a three-scale model that combines crystal plasticity, a polycrystalline aggregate model and a periodic homogenization through a Finite Element unit cell for the composite analysis. (10.1016/j.ijplas.2003.09.001)
  DOI : 10.1016/j.ijplas.2003.09.001
• A computational approach to thermomechanical fatigue
  
  • Constantinescu Andrei
  • Charkaluk Eric
  • Lederer Guy
  • Verger Laetitia
  International Journal of Fatigue, Elsevier, 2004, 26, pp.805-818. This paper presents a computational approach for the lifetime assessment of structures under thermomechanical loading. One of the main features of the work is the search for simplicity and robustness in all steps of the modeling, in order to match the proposed method with industrial constraints. Among the peculiarities of the engineering environment are the imposed commercial computer programs and the short time delays for manufacturing. The proposed method is composed of a fluid flow, a thermal and a mechanical finite element computation, as well as a final fatigue analysis. The efficiency of the approach is proved by comparison with experimental results on prototype manifolds. The numerical results match both the localization of the damage zone and the lifetime. (10.1016/j.ijfatigue.2004.01.006)
  DOI : 10.1016/j.ijfatigue.2004.01.006
• Optimisation des portiques élastoplastiques : état limite des portiques élastoplastiques sous chargement répété mobile
  
  • Adjovi Edmond Codjo
  • Gnanvo Cyprien
  • Foudjet Amos
  • Halphen Bernard
  Journal des Sciences pour l'Ingénieur, 2004, 4, pp.50-59. La présente étude propose la généralisation de la notion de l'état d'auto contrainte de provenance statique des contours fermés au premier théorème d'adaptation "Bleich–Melan" pour l'analyse élastoplastique des portiques sous un système de charges répétés mobiles. La formulation adoptée dans ce travail conduit à la programmation linéaire et nécessite l'utilisation de la méthode SIMPLEX. La méthode développée permet de définir l'état de contrainte réel d'un portique donné sous un chargement donné. Les résultats de l'étude sont complétés par une application numérique.
• Initiation and propagation of fracture in the models of Griffith and Barenblatt
  
  • Marigo Jean-Jacques
  • Truskinovsky Lev
  Continuum Mechanics and Thermodynamics, Springer Verlag, 2004, 16, pp.391-409. In the setting of the simplest debonding problem we give a systematic comparison of the fracture models due to Griffith and Barenblatt. We prove that the Griffith model represents an asymptotic Γ-limit of the Barenblatt model, when the ratio of the external and internal lengths increases indefinitely. We then illustrate the character of convergence by solving explicitly two sample problems with “initially rigid” and “initially elastic” cohesive energies. The geometrical simplicity of the setting allows us to study the small parameter dependence of both global and local minimizers of the total energy. (10.1007/s00161-003-0164-y)
  DOI : 10.1007/s00161-003-0164-y
• L'EBSD: un outil pour la micromécanique des materiaux
  
  • Caldemaison D.
  • Crépin Jérôme
  • Dexet M.
  • Gélébart L.
  , 2004, pp.87-100.
• Simulating wear under cyclic loading by a minimization approach
  
  • Peigney Michaël
  International Journal of Solids and Structures, Elsevier, 2004, 41, pp.6783-6799. A new method is developed to determine the asymptotic state reached by a solid continuum subjected to wear and submitted to a cyclic loading. The main idea is to express the stabilized state as the solution of a minimization problem. This approach is applied to the wear problem of a half-plane in contact with a cyclically moving indenter. (10.1016/j.ijsolstr.2004.05.022)
  DOI : 10.1016/j.ijsolstr.2004.05.022
• Microstructure Influence on Damage Initiation in Zirconium Alloys
  
  • Elbachiri Kamal
  • Crépin Jérôme
  • Bretheau Thierry
  • Rebeyrolle Véronique
  , 2004.
• Nanocomposites base polymère renforcés par des particules rigides
  
  • Chabert Emmanuelle
  • Chazeau Laurent
  • Gauthier Catherine
  • Dendievel Rémy
  • Cavaillé Jean-Yves
  Mechanics & Industry, EDP Sciences, 2004, 5, pp.489-496. Les matériaux composites à base polymère montrent, dans certains cas, des comportements mécaniques spécifiques lorsque la taille des renforts particulaires rigides devient nanométrique. Il semble que cette particularité provienne du fait que les distances inter-particulaires moyennes sont alors comparables aux dimensions caractéristiques des chaînes polymères. On observe parfois des effets de renfort beaucoup plus importants que pour des composites classiques qui peuvent être attribués à l'existence de réseaux particule/macromolécule/particule ou encore de réseaux rigides de particules. Dans cette courte revue, l'effet du facteur de forme, de la fraction volumique et du procédé de mise en oeuvre sont discutés, ainsi que l'état de l'art en ce qui concerne la modélisation dans les domaines linéaire et non linéaire. (10.1051/meca:2004049)
  DOI : 10.1051/meca:2004049
• 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.
• 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
• 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
• 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
• 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