Publications

2002

• Approche locale de la déformation d'alliage de structure hexagonale
  
  • Bornert Michel
  • Bretheau Thierry
  • Caldemaison Daniel
  • Crépin Jérôme
  • Doumalin Pascal
  , 2002, 90 (5-6), pp.88-92. Cette étude s’intéresse à la compréhension des mécanismes de déformation d’alliages de zirconium en relation avec la microstructure et leurs conséquences vis à vis de l’endommagement du matériau. Grâce à une approche micromécanique, il a été possible d’identifier les mécanismes de déformation activés, de déterminer leur cission critique d’activation ainsi que de mettre en évidence l’existence d’une interaction à “méso-échelle”, observable à l’aide de cartes de déformation et de covariogrammes. (10.1051/mattech/200290050088)
  DOI : 10.1051/mattech/200290050088
• 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.
• 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.
• Infrared thermography of 3D-woven fabrics subjected to service loading
  
  • Gorog Sylvie
  • Luong Minh-Phong
  • Eytard Jean-Christophe
  , 2002, pp.1383-1386. The paper introduces the use of an infrared thermographic technique to detect the manifestation of physical processes of damage in a three-dimensional woven polyester fabric subjected to the traffic of heavy vehicles. Thanks to the thermomechanical coupling occurring in the polyester fabric, this non-destructive, noncontact and in real time technique (NDT) highlights the heat generation caused by the energy dissipated by the material during the passage of a wheel. Experimental results show that the infrared thermographic technique provides a useful means to evaluate the mechanical performance of geosynthetic products under full-scaleservice loading.
• Mechanical model of the inspiratory pump
  
  • Basso Ricci Sergio
  • Cluzel Philippe
  • Constantinescu Andrei
  • Similowski Thomas
  Journal of Biomechanics, Elsevier, 2002, 35, pp.139-145. The inspiratory pump (inspiratory muscles and the rib cage) translates inspiratory commands in alveolar ventilation by applying expanding forces to the lungs. Its functioning is of paramount importance to the physiology of breathing and of many pathological situations. Major difficulties in studying its function in relationship with its structure arise from the extremely complex geometrical disposition of its active and passive elements. We herein describe a two-compartment model of the inspiratory pump, with model parameters identification derived from actual measurements obtained by magnetic resonance imaging in normal humans. The equations governing the model are presented. Numerical simulations validate the model by showing a behaviour similar to physiological observations. This opens the possibility of predicting the behaviour of the respiratory system during diseases involving changes in its mechanical or geometrical characteristics. (10.1016/S0021-9290(01)00164-6)
  DOI : 10.1016/S0021-9290(01)00164-6
• 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.
• Infrared observation of thermomechanical couplings in solids
  
  • Luong M. P.
  , 2002, pp.492-506. No abstract provided
• Direct evaluation of double hypersingular integrals and new free terms in 2D symmetric Galerkin BEM
  
  • Bonnet Marc
  • Guiggiani Massimo
  , 2002. In this paper a new general algorithm is developed for the direct evaluation of all singular double integrals arising in the 2D Galerkin BEM, including those with hypersingular kernels. A distinguishing feature of the proposed method is that double singular integrals are treated as a whole, that is, not as inner integrals followed by outer ones. Therefore, when applied to the symmetric Galerkin BEM, the proposed technique is strictly symmetry preserving. Moreover, a careful analysis of the limiting process is performed which shows that some new free terms may arise. (10.1016/S0045-7825(03)00286-X)
  DOI : 10.1016/S0045-7825(03)00286-X
• Pattern-based modelling of composite materials; principles, applications and limitations
  
  • Bornert Michel
  , 2002. No abstract provided
• Effet de la répartition hétérogène en amas des particules de MnS sur la rupture fragile et ductile des aciers de cuve
  
  • Bilger N.
  • Bornert Michel
  • Auslender F.
  • Masson Renaud
  • Michel J. C.
  • Moulinec H.
  • Suquet P.
  • Zaoui Z.
  , 2002. No abstract provided
• New bounds and estimates for porous media with rigid perfectly plastic matrix
  
  • Bilger Nicolas
  • Auslender François
  • Bornert Michel
  • Masson Renaud
  Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, Elsevier, 2002, 330, pp.127-132. We derive new rigorous bounds and self-consistent estimates for the effective yield surface of porous media with a rigid perfectly plastic matrix and a microstructure similar to Hashin's composite spheres assemblage. These results arise from a homogenisation technique that combines a pattern-based modelling for linear composite materials and a variational formulation for nonlinear media. (10.1016/S1631-0721(02)01438-9)
  DOI : 10.1016/S1631-0721(02)01438-9
• An optimisation method for separating and rebuilding one-dimensional dispersive waves from multi-point measurements
  
  • Bussac Marie-Noël
  • Collet Pierre
  • Gary Gérard
  • Othman Ramzi
  Journal of the Mechanics and Physics of Solids, Elsevier, 2002, 50 (2), pp.321-349. When using a classical SHPB (split Hopkinson pressure bar) set-up, the useful measuring time is limited by the length of the bars, so that the maximum strain which can be measured in material testing applications is also limited. In this paper, a new method with no time limits is presented for measuring the force and displacement at any station on a bar from strain or velocity measurements performed at various places on the bar. The method takes the wave dispersion into account, as must inevitably be done when making long time measurements. It can be applied to one-dimensional and single-mode waves of all kinds propagating through a medium (flexural waves in beams, acoustic waves in wave guides, etc.). With bars of usual sizes, the measuring time can be up to 50 times longer than the time available with classical methods. An analysis of the sensitivity of the results to the accuracy of the experimental data and to the quality of the wave propagation modelling was also carried out. Experimental results are given which show the efficiency of the method. (10.1016/S0022-5096(01)00057-6)
  DOI : 10.1016/S0022-5096(01)00057-6
• Behaviour characterization of polymeric foams over a large range of strain rates
  
  • Zhao Han
  • Gary Gérard
  International Journal of Vehicle Design, Inderscience, 2002, 30, pp.135-145. The testing and modelling of the mechanical behaviour of some polymeric foams involved in the automotive industry are presented. A variety of current experimental arrangements over a large range of strain rates have been reviewed. Recent improvements of a particularly useful technique for impact loading–the split Hopkinson bar–are presented. A phenomenological model is developed to describe experimental data. Difficulties for 3-dimensional testing and modelling are also discussed. (10.1504/IJVD.2002.002028)
  DOI : 10.1504/IJVD.2002.002028
• Micromechanical study of abnormal fatigue cracking of Ti6246 at high Kmax
  
  • Mignot F.
  • Doquet V.
  • Baudoux C.
  • Petit J.
  , 2002, pp.1773-1780. During cyclic tests performed with a constant Kmax and increasing Kmjn on a α/β titanium alloy, if Kmax is higher than 60-70% of Klc the crack growth rate does not drop, as normally expected, but reaches an asymptotic value. Solute hydrogen is shown to segregate at the crack tip when the cyclic plastic zone vanishes and to enhance room temperature creep, strain localisation and decohesion along α/β interfaces. (10.1515/JMBM.2005.16.3.195)
  DOI : 10.1515/JMBM.2005.16.3.195
• Transition vers une onde glissement-adhérence-décollement sous contact frottant de Coulomb
  
  • Oueslati A.
  • Baillet L.
  • Nguyen Q. S.
  , 2002, pp.155-162. No abstract provided
• Analysis of the numerical instabilities in the hydrocodes when using an elasto­viscoplastic behaviour
  
  • Mouro P.
  • Gary G.
  , 2002. No abstract provided
• Optimal reliability of metallic structures during variable amplitude loadings
  
  • Zarka Joseph
  • Karaouni Habib
  , 2002.
• Principes variationnels et exploitation de mesures de champs en élasticité
  
  • Bonnet Marc
  • Bui Hui Duong
  • Constantinescu Andrei
  , 2002, 4 (6), pp.687-697. Il est parfois nécessaire d'identifier certaines grandeurs ou certains paramètres caractérisant des structures ou des matériaux. Cela passe dans tous les cas par l'exploitation de données expérimentales, et les mesures de champs, par la richesse des informations fournies, sont particulièrement bien adaptées à ces objectifs. Cet article a pour objet de présenter certaines techniques d'inversion particulièrement adaptées à l'exploitation de mesures de champs. L'identification de champs de modules élastiques est choisie comme un problème modèle commode pour l'exposition, mais d'autres problèmes d'identification peuvent être abordés dans le même esprit. On s'efforce en particulier de montrer que l'identification par exploitation de mesures de champs ne doit pas nécessairement se faire par la minimisation de critères de type moindres carrés sur les observations, car le fait de disposer de champs mesurés permet de définir d'autres critères, d'une part adaptés à ce type de données et d'autre part obtenus comme conséquences directes des principes variationnels de l'élasticité. Les critères considérés ici sont principalement l'erreur en relation de comportement et l'écart à la réciprocité. Divers exemples d'illustration, de nature purement numérique pour la plupart, sont présentés. (10.1016/j.mecind.2003.09.011)
  DOI : 10.1016/j.mecind.2003.09.011
• The use of inverse methodologies in geotechnical problems
  
  • Tavares de Castro António
  • Lenao N. S.
  • Ribeiro E Sousa Luís
  • Desheng Defeng
  • Nguyen-Minh D.
  ISRM News journal, 2002, 7, pp.24-32. Back analysis problems, also known as inverse problems or characterization problems, can be formulated as parameter estimation problems, by which means two basic types of problems can be solved: i) Determination of external loads from the structural properties and from observed response, sometimes called inverse problems of the first kind; ii) Determination of structural properties parameters as a function of the external loads and observed responses, sometimes called inverse problems of the second kind. The structural properties are defined by the geometry of the structure and by the properties and zoning of the different constituent materials. The observed effects (displacements, unit strains, stresses, etc.) represent the structural response. The former type of problems corresponds to the determination of the actions on basis of structural properties and of observed effects, whereas the latter refer to the deter­ mination of the characteristics parameters of the structural properties on basis of actions and corresponding observed effects. Back analysis problems can be solved in two ways, which Cividini calls direct approach and inverse approach (Cividini et al., 1981). The direct approach uses the same numerical solutions as the direct analysis, determining the val­ ues of the parameters in accordance to some identi­fication criteria, corresponding, for instance, to the least square, Markov or maximum likelihood meth­ ods (Eykhoff, 1974). The inverse approach requires a reformulation of the problem equations in such a form that the observed effects correspond to known quantities whereas the parameters to be identified appear as unknown. Direct approach methodologies allow the identi­fication of model parameters related with actions or with structural properties (in particular, with mater­ ial properties), which includes the combined use of a numerical model and of an adequate minimiza­tion method. This approach is less sensitive to the quality of the observed values and to the degree of approximation of the numerical model. An impor­tant feature of these methodologies is the separate use of the numerical model and of the minimiza­tion method, which allow the use of complex mod­ els developed in commercial programs (without access to its code). Inverse approach methodologies allow, in princi­ple, faster convergence taxes than direct approach methodologies. Nevertheless, these methodologies are more sensitive to the quality and to the quanti­y of the observed effects and require numerical models that can reproduce approximately the observed response. Usually, the resolution of specif­ ie problems requires the development of specific codes since it is difficult or even impossible to adapt commercial programs to this purpose. In the next paragraphs three different back analysis approaches will be presented.
• Utilisation de symétries géométriques totales ou partielles dans la méthode variationnelle des éléments de frontière
  
  • Bonnet Marc
  , 2002.
• Some examples of friction-induced vibrations and instabilities
  
  • Moirot Franck
  • Nguyen Quoc-Son
  , 2002, pp.137-179. Some examples of friction-induced vibrations and instabilities of elastic structures in unilateral contact are discussed in this paper. The case of an elastic solid in contact with a moving (rigid or elastic) obstacle is considered. The onset of instability and the transition to a dynamic regime is the underlying centre of interest of the discussion. Part 1 gives an overview of some classical and basic results concerning the stability analysis of an equilibrium. The linearization method and Liapunov’s theorem are first recalled. The possibility of Hopf’s bifurcation is considered when there is flutter instability. For time-independent standard dissipative systems, the description of the rate problem and the criteria of static stability and rate uniqueness in the sense of Hill are discussed. Part 2 deals with the instability of the steady sliding of an elastic structure in contact with friction with a rigid or elastic obstacle. Closed-form solutions are discussed for some simple systems and for the problem of frictional contact of elastic layers. The possibility of stick-slip vibrations is discussed in Part 3 in an analytical example of two encased cylinders. The existence of a family of stick-slip waves propagating at constant velocity and with positive slip is discussed. Part 4 addresses the problem of brake squeal as a direct application of the theoretical analysis. This phenomenon is interpreted here as a consequence of the flutter instability of the steady sliding solution. A numerical analysis by the finite element method is performed to compute the steady sliding solution and to discuss its stability for an automotive disk brake. (10.1007/978-3-7091-2534-2_4)
  DOI : 10.1007/978-3-7091-2534-2_4
• Thermal and thermoelastic behaviour of multiply coated inclusion-reinforced composites
  
  • Hervé E.
  International Journal of Solids and Structures, Elsevier, 2002, 39, pp.1041-1058. This work is devoted first to the derivation of the temperature field in an infinite medium constituted of an n-layered isotropic spherical inclusion, embedded in a matrix subjected to a uniform temperature gradient at infinity, under assumptions of no coupling between mechanical and thermal effects and of steady state conditions. These results lead to an estimate of the effective thermal conductivity coefficient of an n-layered inclusion-reinforced material. The second objective of this work is the derivation of the thermoelastic stress and strain fields in the same basic configuration but now, a coupling between stress and thermal properties is considered and the infinite matrix is stress free and subjected to a uniform change of temperature. These results and the solution of the same problem with a hydrostatic loading are used to estimate the effective thermal expansion coefficient and the specific heats for heterogeneous inclusion-reinforced materials. (10.1016/S0020-7683(01)00257-8)
  DOI : 10.1016/S0020-7683(01)00257-8
• 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
  Key Engineering Materials, Trans Tech Publications, 2002, 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