Publications

2002

• Cracking behaviour of PVD tungsten coatings deposited on steel substrates: the influence of film thickness
  
  • Ganne Thomas
  • Crépin Jérôme
  • Serror Serge
  • Zaoui André
  Acta Biomaterialia, Elsevier, 2002, 50, pp.4149-4163. Tungsten coatings have been deposited on steel substrates by magnetron sputtering. For the same processing conditions, the increase of the coating thickness enhances the (111) component of the crystallographic texture whereas the residual stress level decreases. Tensile and four-point bending tests, associated with an acoustic emission analysis, have been performed inside a SEM chamber in order to study the cracking mechanisms. When the residual stresses are taken into account, an intrinsic critical cracking stress and the associated energy release rate can be determined; the obtained values suggest an intergranular cracking mechanism. No debonding has been observed at the interface despite the large plastic deformation of the substrate at the crack tips. The observed strain localisation modes in the substrate near the interface have been shown to have a major influence on the limit crack density. (10.1016/S1359-6454(02)00256-2)
  DOI : 10.1016/S1359-6454(02)00256-2
• On the determination of elastoviscoplastic constants of hard marls from in situ measurements performed on a motorway tunnel in the Alps
  
  • Lecampion Brice
  • Constantinescu Andrei
  • Nguyen Minh Duc
  • Allagnat D.
  , 2002, pp.251-258.
• Simulation numérique d'un disque de frein automobile par une méthode de calcul eulérien
  
  • Nguyen-Tajan Thi Mac-Lan
  • Thomas Jean-Jacques
  • Maitournam Habibou
  , 2002, pp.131-138.
• Détermination de la réponse asymptotique d'une structure anélastique sous chargement thermomécanique cyclique
  
  • Maitournam Habibou
  • Pommier Benjamin
  • Thomas Jean-Jacques
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2002, 330, pp.703-708. Cet article présente une solution alternative aux méthodes classiques (comme la méthode incrémentale) de résolution de problèmes thermomécaniques cycliques non-linéaires. Il s'agit d'une Méthode Cyclique Directe qui consiste à rechercher directement la solution asymptotique d'une structure anélastique soumise à un chargement thermomécanique périodique, sans suivre l'histoire du chargement. Elle est fondée sur le Grand Incrément de Temps et la périodicité de l'état limite et la transformation de Fourier. (10.1016/S1631-0721(02)01516-4)
  DOI : 10.1016/S1631-0721(02)01516-4
• Caractérisation expérimentale de paramètres thermomécaniques liés au frottement
  
  • Stalin Nadine
  • Eytard Jean-Christophe
  Mechanics & Industry, EDP Sciences, 2002, 3, pp.267-270. Les progrès technologiques accomplis en matière de thermographie infrarouge offrent aujourd'hui des possibilités accrues d'étudier des phénomènes thermiques dans le domaine de la mécanique du contact notamment lorsqu'il y a du frottement. Le coefficient de frottement instantané, pouvant varier continûment, est souvent difficile à évaluer. La mise au point d'une méthode basée sur l'émission infrarouge, qui s'appuie sur l'observation conjointe et en continu du coefficient de frottement et des élévations de température au cours d'un essai d'usure en glissement total, permet de disposer d'une autre technique d'évaluation du frottement. Cette démarche expérimentale met en évidence une similitude de comportement, en temps réel, de ces deux facteurs. Les variations de température résultant de la production de chaleur générée par le frottement sont mesurées sur la face opposée à celle du contact. Cette démarche utilise les propriétés de transfert de chaleur par conduction à travers l'épaisseur de l'éprouvette. Cette approche ouvre des perspectives de recherche notamment dans des domaines de la mécanique où les phénomènes se produisent dans des zones de contact difficiles d'accès.
• Using Domain Knowledge in Evolutionary System Identification
  
  • Schoenauer Marc
  • Sebag Michèle
  , 2002. Two example of Evolutionary System Identification are presented to highlight the importance of incorportaing Domain Knowledge: the discovery of an analytical indentation law in Structural Mechanics using constrained Genetic Programming, and the identification of the repartition of underground velocities in Seimsi Prospection. Critical issues for sucessful ESI are discussed in the light of these results.
• Numerical identification of planar cracks in elastodynamics using the reciprocity gap
  
  • Bui Huy Duong
  • Constantinescu Andrei
  • Maigre Hubert
  , 2002, pp.55-60.
• A novel inverse problem in medical emission imaging
  
  • Nguyen Maï K.
  • Truong Tuong Trong
  • Bui Huy Duong
  , 2002, pp.397-404.
• Exploitation of full or partial geometrical symmetry in Symmetric Galerkin BEM
  
  • Bonnet Marc
  , 2002. Procedures based on group representation theory, allowing the exploitation of geometrical symmetry in symmetric Galerkin BEM formulations, are developed for 3D Neumann elastostatic problems, considered as model problems. Both Abelian and non-Abelian finite symmetry groups are considered. More- over, the formulation is developed under the weaker assumption of partial geometrical symmetry, where the boundary has two disconnected components, one of which is symmetric. Numerical examples for partial geometrical symmetry and Abelian and non-Abelian groups demonstrate the effectiveness of the approach. (10.1002/nme.716)
  DOI : 10.1002/nme.716
• Formulation and well-posedness of impact problems in solid mechanics
  
  • Ballard Patrick
  , 2002.
• Compact Unstructured Representations for Evolutionary Design
  
  • Hamda Hatem
  • Jouve François
  • Lutton Evelyne
  • Schoenauer Marc
  • Sebag Michèle
  Applied Intelligence, Springer Verlag, 2002, 16, pp.139-155. This paper proposes a few steps to escape structured extensive representations for objects, in the context of evolutionary Topological Optimum Design (TOD) problems : early results have demonstrated the potential power of Evolutionary methods to find numerical solutions to yet unsolved TOD problems, but those approaches were limited because the complexity of the representation was that of a fixed underlying mesh. Different compact unstructured representations are introduced, the complexity of which is self-adaptive, i.e. is evolved by the algorithm itself. The Voronoi-based representations are variable length lists of alleles that are directly decoded into object shapes, while the IFS representation, based on fractal theory, involves a much more complex morphogenetic process. First results demonstrates that Voronoi-based representations allow one to push further the limits of Evolutionary Topological Optimum Design by actually removing the correlation between the complexity of the representations and that of the discretization. Further comparative results among all these representations on simple test problems seems to indicate that the complex causality in the IFS representation disfavor it compared to the Voronoi-based representations. (10.1023/A:1013666503249)
  DOI : 10.1023/A:1013666503249
• Dynamics of rigid bodies systems with unilateral or frictional constraints
  
  • Ballard Patrick
  , 2002, pp.3-87. The classical theory of rigid bodies systems dynamics is extended into two directions. First, systematic formulation of the dynamics of systems undergoing perfect unilateral constraints is derived. The general admissible form of the impact constitutive equation is obtained. Well-posedness of the evolution problem is proved under the assumption that the data are analytic. Second, systematic formulation of systems undergoing frictional bilateral constraints is discussed. Well-posedness of the associated evolution problem is also demonstrated. (10.1007/978-1-4757-4435-4_1)
  DOI : 10.1007/978-1-4757-4435-4_1
• Parameter Identification for lined tunnels in a viscoplastic medium
  
  • Lecampion Brice
  • Constantinescu Andrei
  • Nguyen Minh Duc
  International Journal for Numerical and Analytical Methods in Geomechanics, Wiley, 2002, 26 (12), pp.1191-1211. This paper is dedicated to the identification of constitutive parameters of elasto‐viscoplastic constitutive law from measurements performed on deep underground cavities (typically tunnels). This inverse problem is solved by the minimization of a cost functional of least‐squares type. The exact gradient is computed by the direct differentiation method and the descent is done using the Levenberg–Marquardt algorithm. The method is presented for lined or unlined structures and is applied for an elastoviscoplastic constitutive law of the Perzyna class. Several identification problems are presented in one and two dimensions for different tunnel geometries. The used measurements have been obtained by a preliminary numerical simulation and perturbed with a white noise. The identified responses match the measurements. We also discuss the usage of the sensitivity analysis of the system, provided by the direct differentiation method, for the optimization of in situ monitoring. The sensitivity distribution in space and time assess the location of the measurements points as well as the time of observation needed for reliable identification. (10.1002/nag.241)
  DOI : 10.1002/nag.241
• Fissuration par fatigue en mode II d'un acier maraging. Effets de fréquence et d'environnement
  
  • Doquet Véronique
  Revue de Métallurgie, EDP Sciences, 2002, pp.441-448. Des essais de fissuration par fatigue en mode Il ont été menés sur un acier maraging, à différentes fréquences, sous air ou sous vide. En affectant les conditions tribologiques le long des flancs de fissure, ces variations des conditions expérimentales jouent sur la cinétique de propagation en mode Il et sa stabilité. La mesure des profils de déplacement le long des flancs permet d'estimer ΔKII effectif et d'unifier les données cinétiques obtenues dans des conditions de frottement plus ou moins intense.
• Application de la théorie de l'adaptation à la modélisation de la fatigue
  
  • Dang Van Ky
  Journal de Physique IV Proceedings, EDP Sciences, 2002, 12, pp.11-13. On se propose dans cette communication de présenter une théorie unifiée de la fatigue qui s'appliquerait aussi bien à la fatigue polycyclique qu'à la fatigue oligocyclique en s'appuyant sur les résultats de la théorie de l'adaptation. Cette théorie avait été proposée par les théoriciens de la mécanique pour étudier la réponse asymptotique des structures élastoplastiques sous chargements cycliques. Dans la démarche qui sera développée ici, le matériau est considérée comme une structure. Notre discussion commence par une présentation des phénomènes liés à la fatigue et qui se produisent à différentes échelles (microscopique,mésoscopique et macroscopique) ainsi que par un rappel des différents théorèmes d'adaptation. On revient ensuite sur un critère de fatigue polycyclique sous sollicitation multiaxial, le critère dit de Dang Van, et on montre que ce critère est essentiellement basé sur l'hypothèse de l'adaptation élastique qui sous entend que l'énergie dissipée dans ce processus est bornée. Dans le domaine de la fatigue oligocyclique, des résultats récents montrent qu'il est également possible de parler d'adaptation élastique et plastique aussi bien à l'échelle mésoscopique qu'à l'échelle macroscopique et que l'énergie dissipée accumulée est bornée par l'énergie de rupture. Ceci nous permettra de présenter le critère énergétique qui a été utilisé avec succès dans différentes applications sur structures industrielles. On illustre les concepts introduits en discutant la méthode de détermination de la limite de fatigue par l'utilisation de la thermographie infrarouge. On termine l'exposé en présentant un certain nombre d'applications qui vont de la fatigue à grand nombre de cycles à la fatigue oligocyclique, notamment sous chargements thermomécaniques susceptibles de provoquer des phénomènes de fatigue-fluage. [Pas d'information supplémentaire dans le pdf] (10.1051/jp4:20020468)
  DOI : 10.1051/jp4:20020468
• An elastodynamic boundary element approach to underground cavity detection
  
  • Guzina B. B.
  • Nintcheu Fata S.
  • Bonnet Marc
  , 2002.
• Reliability of structures during random loadings
  
  • Zarka J.
  • Karaouni H.
  , 2002. No abstract provided
• Mécanique des milieux continus
  
  • Salençon J.
  , 2002.
• Calcul à la rupture / Yield design
  
  • Salençon J.
  , 2002.
• Fatigue design of structures under thermomechanical loadings
  
  • Charkaluk Éric
  • Bignonnet André
  • Constantinescu Andreï
  • Dang Van Ky
  Fatigue and Fracture of Engineering Materials and Structures, Wiley-Blackwell, 2002, 25 (12), pp.1199-1206. This paper presents a global approach to the design of structures that experience thermomechanical fatigue loading, which has been applied successfully in the case of cast‐iron exhaust manifolds. After a presentation of the design context in the automotive industry, the important hypotheses and choices of this approach, based on a thermal 3D computation, an elastoviscoplastic constitutive law and the dissipated energy per cycle as a damage indicator associated with a failure criterion, are first pointed out. Two particular aspects are described in more detail: the viscoplastic constitutive models, which permit a finite element analysis of complex structures and the fatigue criterion based on the dissipated energy per cycle. The FEM results associated with this damage indicator permit the construction of a design curve independent of temperature; an agreement is observed between the predicted durability and the results of isothermal as well as non isothermal tests on specimens and thermomechanical fatigue tests on real components on an engine bench. These results show that thermomechanical fatigue design of complex structures can be performed in an industrial context. (10.1046/j.1460-2695.2002.00612.x)
  DOI : 10.1046/j.1460-2695.2002.00612.x
• On some recent trends in modelling of contact fatigue and wear in rail
  
  • Dang Van Ky
  • Maitournam Habibou
  Wear, Elsevier, 2002, 253, pp.219-227. Specific numerical methods for the computational analysis of damage induced in rail by repeated rolling are presented. The calculations of mechanical stabilized states (shakedown, ratchetting) of rail-like structures subjected to moving contact loads are performed using the “stationary methods”. An association of 2-D finite element method, Fourier expansion in the longitudinal direction of the rail and steady-state assumption reduces the computational cost of such procedures. These methods constitute the key for the quantitative prediction of fatigue. Three types of damage (low-, high-cycle fatigue and damage) are encountered. Special attention to high-cycle fatigue is paid, through the use of Dang Van multi-axial fatigue criterion. The 3-D simulations of rolling contact and investigation of rail high-cycle fatigue illustrate the applicability of the methodology. (10.1016/S0043-1648(02)00104-7)
  DOI : 10.1016/S0043-1648(02)00104-7
• Formulation and Well-Posedness of Unilateral Multibody Dynamics
  
  • Ballard Patrick
  , 2002, 103, pp.25-32. The classical theory of rigid bodies systems undergoing perfect bilateral constraints has received firm mathematical foundations for a long time. We extend it to the case where there are perfect unilateral constraints also. The formulation follows the line initiated by Schatzman (1978) and Moreau (1983). We give a parametrization-free formulation and try to identify the most general form of impact constitutive equation which is compatible with well-posedness. Then, well-posedness is proved under the assumption of analyticity of the data, since it is known, thanks to Bressan (1960) and Schatzman (1978), that uniqueness does not hold in the C∞ setting. (10.1007/978-94-017-1154-8_3)
  DOI : 10.1007/978-94-017-1154-8_3
• Application du contrôle optimal à l'identification d'un chargement thermique
  
  • Delattre Benoît
  • Ivaldi Damien
  • Stolz Claude
  Revue Européenne des Éléments Finis, HERMÈS / LAVOISIER, 2002, 11, pp.393-404. La détermination du champ de température sur certaines pièces d'un moteur est obtenue par la résolution d'un problème inverse. Une alternative aux méthodes expérimentales coûteuses utilisées aujourd'hui est la méthode du contrôle optimal qui permet d'estimer le champ de température à partir de quantités mesurées sur pièce. Différents tests préfigurent des possibilités de prédiction et de fiabilité de la méthode. (10.3166/reef.11.393-404)
  DOI : 10.3166/reef.11.393-404
• An integral formulation for steady-state elastoplastic contact over a coated half-plane.
  
  • Dong C.
  • Bonnet Marc
  Computational Mechanics, Springer Verlag, 2002, 28, pp.105-121. A boundary-domain integral equation for a coated half-space (elastically isotropic homogeneous substratum, possibly anisotropic coating layer) is developed. The half-space fundamental solution is used, so that the discretization is limited to the potential contact zone (boundary elements), the potentially plastic part of the substratum and the coating layer (domain integration cells). Steady-state elastoplastic analysis is implemented within this framework, for plane-strain conditions, for solving rolling and/or sliding contact problems, where at the moment the contact load comes from either a purely elastic contact analysis or is of Hertz type. The constitutive integration is of implicit type. In order to improve accuracy and computational efficiency, infinite elements are used. Comparison of numerical results with other sources, when available, is satisfactory. The present formulation is also used to compute the contact pressure for an isotropic (or anisotropic) coating on an isotropic homogeneous half-space indented by an elastic punch. (10.1007/s00466-001-0274-y)
  DOI : 10.1007/s00466-001-0274-y
• BEM and shape sensitivity techniques in defect identification problems
  
  • Bonnet Marc
  , 2002.