Publications

2000

• 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
• 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
• 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 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
• Etude expérimentale du comportement dynamique des matériaux
  
  • Gary Gérard
  • Zhao H.
  Mechanics & Industry, EDP Sciences, 2000, 1, pp.15-26. Le présent document rappelle la problématique des essais dynamiques, en particulier lorsqu'ils ont pour objet d'étudier le comportement des matériaux. Une attention particulière est portée au système des barres de Hopkinson en raison de son utilisation fréquente dans une gamme de vitesses de déformation allant de 50/s à 5000/s qui correspond à la gamme de vitesses de la plupart des applications industrielles civiles. On rappelle le principe de la mesure telle qu'elle est effectuée avec ce système, ses limites et ses points forts. Elle est ensuite illustrée par quelques résultats typiques obtenus sur divers matériaux et sur des structures à échelle réduite.
• 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
• 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.
• 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
• Thermographie infrarouge des bétons et des structures en bétons
  
  • Luong M. P.
  , 2000. No abstract provided
• Using full or partial geometrical symmetry in symmetric Galerkin BEM formulations
  
  • Bonnet Marc
  , 2000.
• Identification d'une distribution axisymétrique de contraintes de contact élastique
  
  • Ben Abdallah Jallel
  • Bonnet Marc
  , 2000.
• Modeling of the thermomechanical behaviour of a 7xxx aluminum alloy in welding conditions
  
  • Aubert S.
  • Archambault P.
  • Stolz Claude
  • Petitpas E.
  , 2000.
• 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
• 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
• 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
• 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