Publications

2002

• 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
• BEM and shape sensitivity techniques in defect identification problems
  
  • Bonnet Marc
  , 2002.
• 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
• 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
• 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
• 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
• Formulation and well-posedness of impact problems in solid mechanics
  
  • Ballard Patrick
  , 2002.
• A novel inverse problem in medical emission imaging
  
  • Nguyen Maï K.
  • Truong Tuong Trong
  • Bui Huy Duong
  , 2002, pp.397-404.
• Numerical identification of planar cracks in elastodynamics using the reciprocity gap
  
  • Bui Huy Duong
  • Constantinescu Andrei
  • Maigre Hubert
  , 2002, pp.55-60.
• 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
• 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.
• 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.
• 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
• 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
• Analysis of the numerical instabilities in the hydrocodes when using an elasto­viscoplastic behaviour
  
  • Mouro P.
  • Gary G.
  , 2002. No abstract provided
• 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
• 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
• 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
• 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
• Sensitivity analysis and identification of material defects in dynamical systems
  
  • Burczyński Tadeusz
  • Bonnet Marc
  • Fedeliński Piotr
  • Nowakowski Marek
  Systems Analysis Modelling Simulation, Informa UK (Taylor & Francis), 2002, 42 (4), pp.559-574. This paper deals with an analytical and computation strategy, based on the adjoint variable approach and boundary integral equation (BIE) formulations, for evaluating void or crack shape sensitivities of objective functionals. Boundary-only expressions for such sensitivities are sought in the context of linear elastodynamics. An evolutionary hybrid algorithm with the gradient mutation is employed for the identification of material defects. Numerical tests of sensitivity expressions and identification of an internal crack and void are presented. (10.1080/02329290290031323)
  DOI : 10.1080/02329290290031323