Publications

2000

• Simulation expérimentale du risque
  
  • Luong Minh-Phong
  , 2000, pp.77-106. Cet Atelier a pour but de présenter quelques méthodologies capables de fournir des informations réalistes en vue d’une évaluation quantitative de la vulnérabilité des ouvrages de génie civil face aux risques de dysfonctionnement, de dommage ou de destruction. Cette synthèse résume les diverses contributions et réflexions du groupe de travail en insistant plus particulièrement sur la problématique du risque décrit, l’approche expérimentale proposée, les résultats obtenus sur des exemples précis et les perspectives.
• Simulation numérique d'une clarinette par projection modale
  
  • Facchinetti Matteo Luca
  • Boutillon Xavier
  • Constantinescu Andrei
  , 2000.
• Exploiting partial or complete geometrical symmetry in boundary integral equation formulations of elastodynamic problems
  
  • Bonnet Marc
  , 2000. Procedures based on group representation theory, allowing the exploitation of geometrical symmetry in symmetric Galerkin BEM formulations of 3D elastodynamic problems, are developed. They are applicable for both commutative and noncommutative finite symmetry groups and to partial geometrical symmetry, where the boundary has two disconnected components, one of which is symmetric. (10.1007/978-3-642-56288-4_18)
  DOI : 10.1007/978-3-642-56288-4_18
• Intelligent'' optimal design of materials and structures: what does it mean?
  
  • Zarka Joseph
  , 2000 (DETC2000/DAC-14492). The engineers have to face very important problems in the design, the test, the survey and the maintenance of their structures. These problems did not yet get full answer even from the best people in the world. Usually in these problems (such as no satisfactory constitutive modeling of materials, no real control of the accuracy of the numerical simulations, no real definition of the initial state and/or the effective loading of the structure), there is no solution and the experts do not understand the problem in its whole. Moreover, the available data may be not statistically representative (i.e. are in limited number), fuzzy, qualitative and missing in part. We propose a practical solution the « Intelligent Optimal Design of Materials and Structures » where the actual best knowledges of the researchers/experts are intelligently mixed to the results of experiments or real returns. Several examples of applications are given in this serial set· of papers to explain the real meaning and power of this approach.
• “Intelligent” Optimal Design of Woven Composites
  
  • Zarka Joseph
  • Doux Thierry
  , 2000, pp.275-277. By the coupling of the existing knowledge of experts, the numerical results and the experimental data with the help of some special automatic learning and optimization techniques, it is now possible to propose a very simple tool to design materials. The purpose of this paper is to show its particular application to the very difficult design of woven composites where it is necessary to adjust the mechanical properties, the electromagnetic properties and taking care of the price too. (10.1115/DETC2000/DAC-14494)
  DOI : 10.1115/DETC2000/DAC-14494
• Intelligent modeling of woven materials
  
  • Zarka Joseph
  • Doux Thierry
  , 2000. This paper shows the particular application of the general approach "Intelligent Optimal Design" to the design of a woven composite material used o make radomes and for which the mechanical and electromagnetical properties have to satisfy special properties. Although the design of such a material needs the control of almost 50 design parameters, with a very limited number of examples of materials in the data base, but with a special description of each material, it is possible to extract the rules necessary to predict the behaviour of any new material with a rather good accuracy and thereafter, to reach the optimal design (minimum cost) associated to any new requirements. (10.2514/6.2000-4942)
  DOI : 10.2514/6.2000-4942
• Méthode de Schwarz additive avec solveur grossier pour problèmes non symétriques
  
  • Alart Pierre
  • Barboteu Mikaël
  • Le Tallec Patrick
  • Vidrascu Marina
  Comptes Rendus de l'Académie des Sciences - Series I - Mathematics, Elsevier, 2000, 331 (5), pp.399-404. Dans cette Note, nous présentons la généralisation à la résolution de systèmes non symétriques d'une méthode de décomposition de domaines extensible de type Neumann–Neumann. Cette généralisation a pu être effectuée en utilisant le cadre théorique des méthodes de décomposition en sous-espaces de Schwarz additifs avec introduction d'un espace grossier correctement adapté au cas non symétrique. La méthode développée est testée sur des problèmes non symétriques engendrés par la formulation mixte de problèmes de contact avec frottement. (10.1016/S0764-4442(00)01667-0)
  DOI : 10.1016/S0764-4442(00)01667-0
• Microextensométrie locale par corrélation d'images numériques. Application aux études micromécaniques par microscopie électronique à balayage.
  
  • Doumalin Pascal
  , 2000. Ce travail a vise dans un premier temps au developpement d'une technique de microextensometrie locale par l'adaptation des methodes de correlation d'images numeriques, utilisees depuis plusieurs annees en imagerie optique macroscopique pour determiner des champs de deplacements locaux dans des structures, aux images numeriques obtenues, a echelle bien plus fine, par microscopie electronique a balayage (meb). L'etude a permis de reveler les difficultes specifiques rencontrees pour atteindre la precision theorique de ces techniques avec des images de meb et a conduit a proposer un certain nombre de procedures pour les traiter. On s'est en particulier attache a analyser les defauts d'images induits par les imperfections de balayage du meb, par de tres faibles variations de grandissement ou par la derive du faisceau, a etudier les consequences des reglages non optimaux du meb, conduisant a des niveaux de bruit trop eleves, ou encore l'effet de forme du repere pour marquer les echantillons sur la precision de mesure. Cette technique de microextensometrie a ensuite ete appliquee a l'investigation des mecanismes locaux de deformation dans des materiaux heterogenes, notamment au cours du tout premier stade de l'ecoulement plastique. On s'est interesse plus particulierement a la mise en evidence, la caracterisation, la quantification et enfin la modelisation du phenomene de localisation precoce de la deformation sous forme de bandes dans des materiaux elastoplastiques. Un moyen original pour quantifier statistiquement la portee des bandes a ete propose en appliquant sur le champ de deformation lui-meme les methodes statistiques classiquement utilisees pour caracteriser la distribution des phases.
• Une utilisation de Castem 2000
  
  • Constantinescu Andrei
  , 2000.
• Quantifying Drilling Efficiency and Disruption: Field Data vs. Theoretical Model
  
  • Putot Claude
  • Guesnon Jean
  • Perreau Philippe
  • Constantinescu Andrei
  SPE Drilling and Completion, Society of Petroleum Engineers, 2000, 15 (02), pp.118-125. Mechanical and kinematics data at the bit have been collected during drilling operations and organized to identify optimal drilling efficiency. Transitional conditions towards abnormal behavior have been distinguished. Normal drilling is usually characterized by regular linear relationships between global control variables at the bit, which approximately correspond to an upscaling of a local Mohr-Coulomb-type failure mechanism of the rock. Most of our experimental data confirm this classical disposition. However, considerable departure from these relationships is noted, especially when there is bottomhole assembly (BHA) resonance or when there is partial balling at the bit. The field tests presented here allow us to verify classical theory and to draw up new guidelines for behavior in nonoptimal or dangerous, evolving operating conditions, such as those that occur under poor cleaning conditions. The main features of a mechanical structuring model involving transition towards low-efficiency conditions are presented, and it is shown how this model confirms our interpretation of field data. The model couples the drillability of rock and the general dynamics of the bit in an original and synthetic way. It makes it possible to understand and test the sensitivity of bit response to variables such as "weight on hook," torque on the drillstring, and flow rate of the fluid. (10.2118/64004-PA)
  DOI : 10.2118/64004-PA
• An affine formulation for the prediction of the effective properties of nonlinear composites and polycrystals
  
  • Masson Renaud
  • Bornert Michel
  • Suquet Pierre
  • Zaoui André
  Journal of the Mechanics and Physics of Solids, Elsevier, 2000, 48 (6-7), pp.1203-1227. Variational approaches for nonlinear elasticity show that Hill’s incremental formulation for the prediction of the overall behaviour of heterogeneous materials yields estimates which are too stiff and may even violate rigorous bounds. This paper aims at proposing an alternative ‘affine’ formulation, based on a linear thermoelastic comparison medium, which could yield softer estimates. It is first described for nonlinear elasticity and specified by making use of Hashin–Shtrikman estimates for the linear comparison composite; the associated affine self-consistent predictions are satisfactorily compared with incremental and tangent ones for power-law creeping polycrystals. Comparison is then made with the second-order procedure and some limitations of the affine method are pointed out; explicit comparisons between different procedures are performed for isotropic, two-phase materials. Finally, the affine formulation is extended to history-dependent behaviours; application to the self-consistent modelling of the elastoplastic behaviour of polycrystals shows that it offers an improved alternative to Hill’s incremental formulation. (10.1016/S0022-5096(99)00071-X)
  DOI : 10.1016/S0022-5096(99)00071-X
• Représentations non structurées en optimisation topologique de formes par algorithmes évolutionnaires
  
  • Hamda Hatem
  • Jouve François
  • Lutton Evelyne
  • Schoenauer Marc
  • Sebag Michèle
  , 2000, Canum 2000 : Actes du 32e Congrès national d'analyse numérique, pp.153-179. Les algorithmes évolutionnaires sont des méthodes d'optimisation stochastiques inspirées -- grossièrement -- de l'évolution naturelle des populations. Méthodes globales d'ordre 0, leur robustesse et leur souplesse leur permettent d'attaquer la résolution numérique de problèmes difficiles à résoudre autrement. Mais c'est leur capacité à travailler sur des espaces de recherche non standards qui leur offre les perspectives les plus originales. Dans le domaine de l'optimisation topologique de formes, les résultats obtenus il y a quelques années montraient la faisabilité de l'approche évolutionnaire, mais étaient limités par le fait que la complexité de l'espace de recherche était liée à celle du maillage utilisé lors de la simulation numérique. Ce papier introduit un ensemble de représentations compactes et non structurées dont la complexité n'est pas fixe, mais est ajustée par l'algorithme lui-même. Les résultats présentés dans cet article montrent que leur utilisation permet de repousser les limites de l'optimisation topologique de formes évolutionnaire. Des résultats sur des problèmes test simples tentent ensuite de comparer les mérites des diverses approches proposées.
• On the simulation of large viscoplastic structures under anisothermal cyclic loadings
  
  • Verger Laetitia
  • Constantinescu Andrei
  • Charkaluk Eric
  , 2001, pp.341-350. The optimal design of parts submitted to thermomechanical loadings is a key issue for the safety and quality assessments of structures. In this context, the present paper discusses the choice of a behavior model and the determination of its parameters. For cast iron and aluminum alloy applications, two constitutive laws are compared : one is based on a classical unified viscoplastic model and the other is based on a two-layer plastic-viscous rheological model. The following discussion shows that the use of anisothermal experiments is very important for the identification of material parameters and that simple models can be successfully applied for the predictive lifetime assessments of large 3D structures. (10.1007/978-94-015-9628-2_33)
  DOI : 10.1007/978-94-015-9628-2_33
• Une transformation du problème d'élasticité linéaire en vue d'application au problème de l'inclusion et aux fonctions de Green
  
  • Pouya Ahmad
  Comptes Rendus de l'Académie des Sciences - Series III - Sciences de la Vie, Elsevier, 2000, t 328 (Série II b), pp.437-443. Nous présentons une transformation simple du problème de structure élastique linéaire. Le problème transformé se présente sous forme d'un nouveau problème de structure élastique linéaire avec un comportement, une géométrie et des données de forces et de déplacements imposés différents. Le problème transformé peut être plus simple à traiter ou correspondre à des cas de solutions analytiques connues. A l'aide de cette transformation, on peut ramener le problème de l'inclusion ellipsoïdale en un problème d'inclusion sphérique, étendre les résultats connus pour le tenseur d'Eshelby pour les cas de matrice isotrope ou d'isotropie transverse, à des cas plus larges, et enfin, établir l'expression analytique de la fonction de Green du milieu infini pour des cas de comportements orthotropes plus riches que l'isotropie transverse, ainsi que des cas non orthotropes.
• Numerical lifetime assessment of engine parts submitted to thermomechanical fatigue
  
  • Lederer Guy
  • Charkaluk Eric
  • Verger Laetitia
  • Constantinescu Andrei
  , 2000. In this work a numerical method for the design of components submitted to severe cyclic thermomechanical loading is developed. This tool is based on a Finite Element (FE) analysis. In a first part the temperature distribution is obtained and used in the second part for the mechanical computation. The analyses use the description of the geometry of the part, a precise information of the thermal properties, an appropriate behavior of the material at low and high temperature and a good assessment of the boundary conditions (heat transfer coefficients, contact, …). This method is applied to asses the low cycle fatigue design of a diesel turbo-charged exhaust manifold in cast iron. These calculations, failure location and lifetime estimation, obtained on two versions of this component, are compared to experimental data. The results show a good agreement in terms of critical zones location and of lifetime comparison in both versions and permit thus to classify the versions. (10.4271/2000-01-0789)
  DOI : 10.4271/2000-01-0789
• Low cycle fatigue behaviour of β treated zirconium: partial irreversibility of twinning and consequences for damage
  
  • Crépin Jérôme
  • Bretheau Thierry
  • Caldemaison Daniel
  • Ferrer Franck
  Acta Materialia, Elsevier, 2000, 48, pp.505-516. The aim of this study is to understand the low cycle fatigue behaviour of β treated zirconium. It focuses especially on the contribution of twinning mechanisms. In situ fatigue tests performed inside a scanning electron microscope allow the observation of the activation of twins and their partial reversibility, depending on the applied stress. Moreover, the acoustic signature (shape factor) of the different twinning systems has been characterized allowing the following of inception and evolution of twins during the fatigue tests. Finally, the consequence of such a partial irreversibility on damage and crack localization is shown. (10.1016/S1359-6454(99)00358-4)
  DOI : 10.1016/S1359-6454(99)00358-4
• Structural morphology and relaxation spectra of viscoelastic heterogeneous materials
  
  • Beurthey Stéphan
  • Zaoui André
  European Journal of Mechanics - A/Solids, Elsevier, 2000, 19, pp.1-16. We analytically derive the relaxation spectra of a two-phase isotropic material whose phases are isotropic Maxwell media, according to the classical and to the generalized self-consistent schemes. Whereas these spectra are continuous in both cases, they exhibit strong differences which can be associated with the different underlying morphology, either symmetrical (polycrystal-type) in the first case or asymmetrical (composite-type) in the second case. The treatment is extended to the (N+1)-phase model which allows us to deal with coated inclusions or with an interphase between the matrix and the inclusions: the interphase is shown to strongly modify the resultant spectrum. More general cases are then considered for different kinds of constitutive behaviour as well as for coated fibre reinforced composites. As a whole, the spectral analysis method appears to be an efficient tool for the investigation of the connection between structural morphology and the overall behaviour of viscoelastic heterogeneous materials. (10.1016/S0997-7538(00)00157-1)
  DOI : 10.1016/S0997-7538(00)00157-1
• Tenue d'ancrages LMS sur fonds coralliens indurés
  
  • Luong Minh-Phong
  • Habib Pierre
  Rev. Franç. Géotech., 2000, 89, pp.29-32. Cet article rapporte une expérimentation en vraie grandeur d’un système d’ancrage LMS à forte capacité de tenue dans un fond marin constitué de calcaires coralliens indurés de la Polynésie française. Les résultats ont mis en évidence la possibilité de reprise des efforts dans des zones où la compacité du terrain exclut la mise en œuvre des ancres marines traditionnelles. La sécurité de tenue ne dépend pratiquement pas de la couche superficielle souvent hétérogène. La reprise des efforts verticaux réduit très sensiblement la longueur des lignes de mouillage. Le poids réduit de l’ancrage, grâce à une efficacité exceptionnelle (> 100), est un avantage technique et économique de mise en œuvre, extrêmement appréciable par rapport aux ancres marines de type classique. (10.1051/geotech/1999089029)
  DOI : 10.1051/geotech/1999089029
• Influence des contraintes résiduelles sur le comportement à la fissuration de dépôts de chrome élaboré par PVD
  
  • Ganne T.
  • Crépin Jérôme
  • Zaoui A.
  , 2000. No abstract provided
• A discrete dislocation model of Stage I fatigue crack growth and an analysis of Stage II to Stage I transition at low ΔK₁
  
  • Doquet Véronique
  Journal de Physique IV Proceedings, EDP Sciences, 2000, 10 (PR6), pp.145-150. Simulations of dislocations nucleation and glide ahead of a crystallographic mode II crack are performed for push-pull and reversed torsion. An influence of the normal stress on the friction of crack flanks, as well as on the condition for dislocation emission is introduced. The crack growth rates are deduced from the dislocation fluxes at the crack tip. A comparison between the loading modes is made. Taking into account the presence of grain boundaries, the repeated decelerations and sometimes the arrest that characterise Stage I crack growth are described by the model. An analysis of the transition from mode I to mode II crack growth observed at low ΔK₁ in single crystals is proposed. (10.1051/jp4:2000625)
  DOI : 10.1051/jp4:2000625
• Nondestructive damage evaluation of reinforced concrete structure using infrared thermography
  
  • Luong Minh-Phong
  , 2000, pp.98-107. This paper highlights three advantages of infrared thermography as a nondestructive, non-contact and in real-time technique. It permits first observation of the physical manifestation of damage and the mechanism of failure of concrete, second detection of the occurrence of intrinsic dissipation localization, and third evaluation of the fatigue strength in a very short time, compared to traditional testing techniques. In addition, infrared thermography readily describes the damage location and the evolution of structural failure. The investigated parameter is heat generation due to intrinsic dissipation of concrete subject to compressive loading. Owing to the thermomechanical coupling, this technique provides a simple means for evaluating fatigue strength and for discriminating diverse dissipative phenomena. (10.1117/12.385481)
  DOI : 10.1117/12.385481
• Stability Analysis of Incipient Folding and Faulting of an Elasto-Plastic Layer on a Viscous Substratum
  
  • Leroy Yves
  • Triantafyllidis Nicolas
  , 2000, pp.109-139. The initiation of two modes of instability, viz. folding and faulting, is investigated theoretically for an elasto-plastic, frictional- cohesive layer which is underlain by a viscous substratum. The destabilizing factors that are allowed to come into play are the tectonic stress, buoyancy forces resulting from a gravitationally unstable density stratification, and the redistribution of material at the top surface by erosion and deposition processes. The bending stiffness of the overburden, a non-linear function of stress, has a stabilizing influence. A variational formulation of the stability problem allows one to detect the onset of global modes of instability, such as folds and surface modes for compression as well as neck-type modes for extension. Predictions of these global modes remain valid as long as the local condition of strong ellipticity is satisfied. Failure of this condition marks the onset of discontinuities in the velocity field, which are characteristic of localized faulting. The sensitivity of these predictions to the assumed behaviour of the overburden and substratum materials is explored for a prototype representative of a dip section through the Campos salt basin on the Brazilian continental margin. These results illustrate the importance of a proper selection of analogue materials for the design of physical laboratory models. This point is underscored by employing a deformation theory of plasticity which could be seen to reproduce in a simple manner the accommodation of bulk deformation by slip along a population of pervasive small faults in sedimentary rocks as well as in analogue materials, such as sands, used in the laboratory. A historical account of the use of deformation theories of plasticity in stability analyses and a derivation of the relevant incremental moduli are also given in this paper. (10.1007/978-3-642-59617-9_6)
  DOI : 10.1007/978-3-642-59617-9_6
• Shut-in pressure tests - case studies
  
  • Bérest P.
  • Brouard B.
  • Durup G.
  , 2000, pp.105-125. No abstract provided
• A back analysis method based on virtual work principle - application to some geotechnical problems
  
  • Deng Desheng
  • Nguyen Minh Duc
  , 2000, pp.1339-1346. A back analysis method for geotechnical problems has been proposed on the basis of the Virtual Work Principle, in which the original structural model is compared through an iterative process to a modified model with prescribed field measurements. This method is very robust, stable, effective, and works also for non linear rock mass behaviour. For illustration, this method has been applied to a subsidence problem in a mining area, to a shallow tunnel numerical model, and to a tunnel excavation case history.
• Modeling of the thermomechanical behaviour of a 7xxx aluminum alloy in welding conditions
  
  • Aubert S.
  • Archambault P.
  • Stolz Claude
  • Petitpas E.
  , 2000.