Publications

2000

• Deriving adequate formulations for fluid-structure interaction problems : from ALE to transpiration
  
  • Fanion Thierry
  • Fernández Miguel Angel
  • Le Tallec Patrick
  Revue Européenne des Éléments Finis, HERMÈS / LAVOISIER, 2000, 9 (6-7), pp.681-708. Most formulations describing low speed large displacements fluid-structure interaction problems use a totally lagrangian formulation for the structure, and an Arbitrary Euler Lagrange (ALE) formulation for the fluid. The purpose of the present paper is to review the derivation of such formulations, to describe different time discretisation strategies and to explain the type of numerical problems which arise when implementing these techniques. To overcome all technical difficulties arising when dealing with moving grids, we will also explain how an adequate asymptotic expansion can reduce the problem to a standard problem written on a fixed conf iguration, but using specific transpiration interface boundary conditions. This last formulation is rather popular in the aeronautical community, and will be illustrated by various numerical experiments. (10.1080/12506559.2000.10511481)
  DOI : 10.1080/12506559.2000.10511481
• 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.
• Shut-in pressure tests - case studies
  
  • Bérest P.
  • Brouard B.
  • Durup G.
  , 2000, pp.105-125. No abstract provided
• 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
• 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
• On discontinuous stresses at the interface of a bimaterial thermo-elasto-plastic body
  
  • Bui Huy Duong
  • Taheri Said
  • Dang Van Ky
  Advances in Natural Sciences, 2000, 1, pp.79-84.
• The dynamics of discrete mechanical systems with perfect unilateral constraints
  
  • Ballard Patrick
  Archive for Rational Mechanics and Analysis, Springer Verlag, 2000, 154 (3), pp.199-274. The dynamics of discrete mechanical systems with perfect unilateral constraints is formulated in a very general setting. The well-posedness of the resulting evolution problem is studied. It is proved that existence and uniqueness of a maximal solution is ensured provided strong assumptions are made on the regularity of the data: they are supposed to be analytic. Simple examples show that this regularity assumption may not be relaxed. Sufficient conditions to ensure that the maximal solution is defined for all time are supplied. The continuous dependence of the solution on initial conditions is also studied and the numerical computation of the solution is discussed. (10.1007/s002050000105)
  DOI : 10.1007/s002050000105
• An energetic approach in thermomechanical fatigue for silicium molybden cast iron
  
  • Charkaluk E.
  • Constantinescu Andreï
  Materials at High Temperatures, Taylor and Francis, 2000, 17 (3), pp.373-380. The purpose of this paper is to define a low cycle fatigue criterion in order to predict the failure of engineering structures. The major problem in defining a predictive fatigue criterion is that it should be applicable for structures submitted to complex multiaxial thermo-mechanical loadings but should be identifiable from simple experiments on specimens. After a short critical review of the principal criteria used in low cycle fatigue it will be shown that the dissipated energy per cycle permits a correlation of isothermal and anisothermal results obtained on silicon molybdenum cast iron in the case of specimens and also on structures. (10.1179/mht.2000.17.3.001)
  DOI : 10.1179/mht.2000.17.3.001
• Plan/plan sliding contact modelling by the boundary element method
  
  • Serre Ingrid
  • Bonnet Marc
  • Pradeilles-Duval Rachel Marie
  , 2000.
• Hétérogénéité des contraintes au sein d'un matériau lamellaire. Application à un alliage intermétallique TiAl
  
  • Gélébart Lionel
  • Crépin Jérôme
  • Bretheau Thierry
  • Bornert Michel
  , 2000.
• A plasticity model for discontinua
  
  • Leroy Yves
  • Sassi William
  , 2000, pp.77-107. This article is concerned with the development and application of a simple continuum theory for rocks that may contain both randomly as well as preferentially oriented plane discontinuity surfaces. The theory stipulates that displacement discontinuities are independently activated on these surfaces as soon as an appropriate yield criterion is fulfilled; these displacement jumps account for the irreversible, ‘plastic’ part of the bulk deformation. In stress space, the critical conditions for the activation of discontinuous slip or opening displacements define an overall yield envelope that could be initially anisotropic, reflecting for example a weakness of certain orientations due to pre-existing joint sets. For the yield conditions studied in this paper, essentially a Coulomb-type friction law and a simple fracture opening condition, the inferred stress-strain response under typical triaxial loading conditions reveals the sensitivity of the two discontinuous deformation modes to the confining pressure. The incipient growth of a geological fold in such a material is modelled as a problem of plate bending. The slip- and opening-modes of deformation are found to be activated typically in the fold intrados and extrados, respectively. Under certain conditions, both modes will be activated simultaneously at the same locality and contribute to the total deformation. Field observations on a well exposed sandstone anticline are reported here, which support this conclusion. The present plasticity model for discontinua can clearly be explored in more detail for realistic distributions of faults and joints taken from field observations. It could also be improved in various ways in its description of the underlying deformation mechanisms. Apart from its interest as a mechanical constitutive model, it can also serve as a point of departure for studies of stress-sensitive, anisotropic permeability distributions in fractured formations. (10.1007/978-3-642-59617-9_5)
  DOI : 10.1007/978-3-642-59617-9_5
• An affine formulation for the prediction of the effective properties of nonlinear composites and polycrystals
  
  • Masson Renaud
  • Bornert Michel
  • Suquet Pierre
  • Zaoui André
  , 2000. 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 others an improved alternative to Hill's incremental formulation. (10.1016/S0022-5096(99)00071-X)
  DOI : 10.1016/S0022-5096(99)00071-X
• Dynamic testing at high rates of strain
  
  • Gary G.
  , 2000.
• La programmation logique inductive à la lumière de la transition de phase
  
  • Giordana Attilio
  • Saitta Lorenza
  • Sebag Michèle
  • Botta Marco
  , 2000, pp.157-172. En logique du premier ordre, le test de couverture correspond à un problème de satisfaction de contraintes. Or, dans le domaine de la satisfaction de contraintes, les problèmes les plus difficiles à résoudre en moyenne se concentrent dans une étroite région, appelée transition de phase, qui marque la transition entre les problèmes presque surement satisfiables, et les problèmes presque surement insatisfiables. Pour étudier la complexité et la faisabilité de la Programmation Logique Inductive (PLI), nous avons généré quelques centaines de problèmes d’apprentissage, situés dans et hors de la transition de phase; ces problèmes ont été soumis à FOIL, SMART+ et G-Net. Ces expérimentations systématiques établissent deux résultats. Tout d’abord, la transition de phase constitue un attracteur pour l’apprentissage, dans le sens où toutes les hypothèses produites appartiennent à cette région. En second lieu, une "zone aveugle de l’apprentissage" apparaît: pour tout problème situé dans cette zone, les systèmes de PLI considérés échouent tous à apprendre quelque hypothèse pertinente que ce soit. Ces résultats sont interprétés, et la discussion conduit à remettre en cause les biais usuels de la PLI.
• Self-consistent estimates for nonlinear viscoelastic polycrystals: a simplified resolution of the affine formulation adapted to monotonic loading paths
  
  • Brenner Rénald
  • Castelnau Olivier
  • Masson Renaud
  • Bacroix Brigitte
  • Zaoui André
  , 2000, 177-180, pp.153-158. A simplified resolution of the self-consistent model for non-linear viscoelastic polycrystals is presented. The formulation is based on an affine linearization of the constitutive relations as recently proposed by Masson and Zaoui [4], which adapts Hill's conception of self-consistent modelling to nonlinear viscoelastic behaviours. The approximation of the inverse Laplace-Carson transform introduced here, which is believed to be well adapted to monotonic loading paths, makes the resolution of the whole self-consistent problem possible in the direct time space. This results in a largely simplified numerical algorithm. Comparisons with the predictions of a model treating accurately the inverse Laplace-Carson transform are presented, and very good results are obtained for creep of FCC and HCP polycrystals. (10.4028/www.scientific.net/KEM.177-180.153)
  DOI : 10.4028/www.scientific.net/KEM.177-180.153
• Approche multi-échelle en fatigue polycyclique anisotherme
  
  • Maitournam Habibou
  • Nguyen-Tajan Thi Mac-Lan
  Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, Elsevier, 2000, 328 (5), pp.373-379. Une extension de l'approche macro-méso développée par Dang Van en fatigue isotherme à grand nombre de cycles est proposée dans le cas de structures subissant des chargements cycliques anisothermes et dont les limites de fatigue dépendent de la température. Elle est essentiellement fondée sur l'hypothèse d'adaptation aux échelles macroscopique et mésoscopique. L'utilisation d'une condition locale d'adaptation écrite dans le cas anisotherme conduit à une nouvelle formulation des critères de fatigue. (10.1016/S1620-7742(00)00049-0)
  DOI : 10.1016/S1620-7742(00)00049-0
• Modèles micromécaniques de l'interface d'un système tribologique dans une approche thermodynamique de l'usure continue
  
  • Dragon-Louiset Marta
  Mechanics & Industry, EDP Sciences, 2000, 1 (1), pp.37-42. Cette étude s'inscrit dans une approche énergétique de l'usure de glissement proposant un modèle prédictif du phénomène. Concernant l'interface de deux corps soumis au contact et au frottement, elle cherche à caractériser un comportement moyen et homogénéisé du milieu granulaire, appelé troisième corps. Dans ce cadre, la description de ce milieu comme étant celle d'un fluide visqueux est proposée. On fait l'inventaire de lois de variation de la viscosité d'une suspension avec la fraction volumique des particules qu'elle contient, utilisables dans l'étude du troisième corps.
• Standard dissipative systems and stability analysis
  
  • Nguyen Quoc Son
  , 2000, pp.343-354. Stability and bifurcation analyses are discussed here for time-independent standard dissipative systems of materials and structures. This discussion is illustrated by some simple applications in plasticity and fracture mechanics. (10.1007/0-306-46946-4_26)
  DOI : 10.1007/0-306-46946-4_26
• On Prandl's lifting equation arising in wear mechanics
  
  • Dragon-Louiset Marta
  • Bui Hui Duong
  • Stolz Claude
  Archives of Mechanics, 2000, 52 (4-5), pp.547-567. A sliding wear contact between a rigid punch and an elastic half plane in presence of a thin aggregate film composed of solid debris and a lubricant fluid is studied. The model based on any wear criterion and constitutive law of the film suggested by micromechnanics approximations. The mechanical system is governed by the evolution of the volume fraction of debris, considered as an internal state variable. The key step iterative computations for solving the non linear system of equations is based on the solution of the fundamental integro-differential equation for the compressive normal stress. Uniqueness of the solution of the integrodifferential equation is then proved. It is shown that there is a profound relationship between the latter equation and Prand'l lifting equation in aerodynamics : both equations cn be solved by Chebyshev's series, and experimentally by similar elaectrical setups. Mathematically, it is found that both equations are related to real and imaginary components of some complex potential, respectively, and to weakly adjoint integro-differential oprators.
• Analyzing Relational Learning in the Phase Transition Framework
  
  • Giordana Attilio
  • Saitta Lorenza
  • Sebag Michèle
  • Botta Marco
  , 2000, pp.311-318. A key step of relational learning is testing whether a candidate hypothesis covers a given example. The covering test is equivalent to a Constraint Satisfaction Problem (CSP), which shows a phase transition in correspondence of critical values of some order parameters. This paper investigates the effects of the phase transition in the covering test on the complexity and feasibility of learning in first order logic languages. Several hundreds of artificial learning problems have been generated. FOIL and other learners have been applied to these problems. The experiments show the presence of a failure region, where all considered learners systematically fail to identify the target concept. Furthermore, the phase transition region behaves as an attractor for the learning search, whatever the target concept and the search strategy be. Interpretations of these findings are proposed and discussed.
• Dynamic tensile testing of sheet metal
  
  • Mouro Pierre
  • Gary Gérard
  • Zhao Han
  Journal de Physique IV Proceedings, EDP Sciences, 2000, 10, pp.149-153. The testing of sheet metal at high strain rates requires the use of the SHPB set-up. This technique provides satisfactory results as far as the compression and shear are concerned. A modified SHPB set-up is presented here, which extends the scope of this technique to the tensile loading of sheet metals. In this case, many measurement problems arise due to the way in which the specimen is connected to the bars, which never completely prevents unexpected slipping and is liable to induce interference waves due to an impedance mismatch. The technique described here was based on the "hat specimen" technique proposed by Lindholm [l]. A two-dimensional "hat shaped" specimen is subjected to compression loading. A tensile state is induced in a symmetrically necked area, where higher strains are concentrated. Connecting supports of an appropriate shape are attached to the bars. They have the same impedance as that of the bars to avoid the occurrence of any interference waves. The "hat" shape prevents sliding, and to ensure perfect initial contact conditions, the complete system is elastically pre-stressed. A special method of wave analysis is then used to determine the forces and displacements occurring at the specimen ends from the strain signals recorded in the bars. (10.1051/jp4:2000925)
  DOI : 10.1051/jp4:2000925
• An elasto-plastic modelling for lamellar crystalline materials
  
  • Gélébart L.
  • Bretheau T.
  • Crépin Jérôme
  • Bornert Michel
  , 2000. No abstract provided
• Simulation of hard particle impact on a TI-6Al-4V substrate coated by a tungsten film
  
  • Graff G.
  • Stolz C.
  • Pradeilles Duval R. M.
  • Sainte Catherine M.-C.
  , 2000. No abstract provided
• Thermodynamical description of moving discontinuities : applications to fracture and wear
  
  • Stolz C.
  , 2000. No abstract provided
• Influence of thickness on crystallographic and mechanical properties of PVD tungsten coatings
  
  • Ganne T.
  • Crépin Jérôme
  • Zaoui A.
  • Pradeilles-Duval R. M.
  , 2000, pp.413-418. No abstract provided