Publications

2000

• Investigation expérimentale et modélisation micromécanique de la déformation locale à chaud d'aciers biphasés
  
  • Pinna Christophe
  • Bornert Michel
  , 2000.
• Détection et quantification thermique de particularités d'appui et de lésions superficielles chez les marcheurs de grand fond
  
  • Parganin D.
  • Loizeau J.
  • Luong M. P.
  • Genson F.
  , 2000. No abstract provided
• Brake squeal: a problem of flutter instability of the steady sliding solution?
  
  • Moirot Franck
  • Nguyen Quoc Son
  Archives of Mechanics, Polish Scientific Publishers Pwn, 2000, 52 (4-5), pp.645-661. Brake squeal results from friction-induced vibrations. This phenomenon is considered here and interpreted as a flutter instability of the steady sliding solution of an elastic solid in unilateral contact with friction with a moving obstacle. A mechanical analysis of the governing equations is given, in particular to obtain the steady sliding solution. The stability analysis of this solution is discussed. A numerical analysis by the finite element method is performed in order to compute the steady sliding solution and to discuss its stability for an automotive disk brake. The validation of the numerical procedure is examined in relation with some analytical results of the literature.
• Intelligent optimal design of naval structures: is it possible?
  
  • Zarka Joseph
  , 2000.
• On the determination of elastic coefficients from indentation experiments
  
  • Tardieu Nicolas
  • Constantinescu Andrei
  Inverse Problems, IOP Publishing, 2000, 16, pp.577-588. The main result of this paper is the extension of the adjoint state method to variational inequalities. This is done for the Signorini contact problem (Kikuchi N and Oden J T 1988 Contact Problems in Elasticity: a Study of Variational Inequalities and Finite Element Methods (Philadelphia: SIAM)) and used for the identification of elastic coefficients from an indentation test. The result is obtained by two independent approaches based on the penalized and respectively, mixed formulations of the direct problem, a Signorini contact problem. An important and astonishing result is that the obtained adjoint problem is a linear problem with Dirichlet boundary conditions. This is expected for problems described with variational equalities (Bui H D 1993 Introduction Aux Problèmes Inverses en Mécanique des Matériaux (Paris: Eyrolles) (Engl. Transl. (Boca Raton, FL: CRC Press)), Lions J L 1968 Contrôle Optimal des Systèmes Gouvernés par des Équations aux Dérivées Partielles (Dunod)), but is a new result for problems described with variational inequalities. As an application, the elastic coefficients of an isotropic body have been identified from the knowledge of a displacement-force curve measured during an indentation test. The efficiency of the method is illustrated on numerical examples for the identification of a bimaterial and a functional gradient material. (10.1088/0266-5611/16/3/303)
  DOI : 10.1088/0266-5611/16/3/303
• On the stability of rate-dependent solids with application to the uniaxial plane strain test
  
  • Nestorović Miroslav
  • Leroy Yves
  • Triantafyllidis Nicolas
  Journal of the Mechanics and Physics of Solids, Elsevier, 2000, 48, pp.1467-1491. The linear stability criterion, proposed for structural models in an earlier paper, is now extended for a general class of elastic–viscoplastic continua. The time-dependent trajectories, whose stability is under investigation, are functions of two characteristic times: the relaxation time of the viscous solid and the rate of the applied loading, with their ratio denoted by T. It is assumed that the loading conditions of the trajectory are not modified by the perturbation. The criterion predicts that a solid is initially unstable if there exists a unit norm perturbation in the velocity field whose time derivative is positive. This condition is equivalent to finding a positive eigenvalue in the self-adjoint part of the operator relating the initial first and second rate of the displacement perturbations. If the dominant eigenvalue is obtained from the non self-adjoint operator, the change in sign of its real part is a sufficient condition for instability. For solids with an associated flow rule, it is shown that the exclusion of instability in a trajectory, in the limit of vanishing T, coincides with stability of the corresponding rate-independent solid in the sense of Hill. The theory is applied to the analysis of a finitely strained rectangular block under uniaxial tension and compression, for different elastic–viscoplastic solids of the von Mises and Drucker–Prager type. (10.1016/S0022-5096(99)00094-0)
  DOI : 10.1016/S0022-5096(99)00094-0
• Identification strategies for recovering material parameters from indentation experiments
  
  • Constantinescu Andrei
  • Tardieu Nicolas
  , 2000, pp.181-190. This chapter describes the progress obtained by the authors on the development of a numerical method for the identification of material parameters from indentation experiments. An indentation experiment is performed by pressing a punch on a material sample and measuring the applied force and the indentation depth. The proposed technique minimizes a least squares cost functional using gradient descent methods. In addition, the adjoint state method is extended to variational inequalities and this permits to compute the gradient of the cost functional with low numerical cost. Using this technique, a series of identifications from indentation experiments have been done and their results are discussed in this chapter. Inverse problem is of practical interest as the indentation test does not demand the creation of complicated specimens and is simple to perform. However, the applications are restricted by the difficult mechanical interpretation of the test. (10.1016/B978-008043693-7/50091-X)
  DOI : 10.1016/B978-008043693-7/50091-X
• Elasticity: Thermodynamic Treatment
  
  • Zaoui André
  • Stolz Claude
  , 2000, pp.2445-2449. The elastic behavior of materials is usually described by direct stress±strain relationships which use the fact that there is a one-to-one connection between the strain and stress tensors $\varepsilon$ and $\sigma$; some mechanical elastic potentials can then be defined so as to express the stress tensor as the derivative of the strain potential with respect to the strain tensor, or conversely the latter as the derivative of the complementary (stress) potential with respect to the former. Nevertheless, these potentials are restricted to specific thermodynamic conditions. This purely mechanical treatment may be generalized and improved by integrating its temperature dependence and by connecting the elastic potentials with the classical thermodynamic functions within a consistent thermodynamic framework. This leads to a more general definition of thermoelasticity (Sect. 1), which can be used for a better understanding of the properties of the elastic moduli (Sect. 2), for a natural definition of rubber elasticity (Sect. 3), and for the prediction of the effective thermal expansion coefficients of heterogeneous materials (Sect. 4). (10.1016/B0-08-043152-6/00436-8)
  DOI : 10.1016/B0-08-043152-6/00436-8
• Cavités de stockage dans le sel : évaluation de l'étanchéité
  
  • Bérest P.
  , 2000, pp.115-134. No abstract provided
• Experimental investigation and micromechanical modeling of the hot deformation of duplex stainless steels
  
  • Pinna C.
  • Bornert Michel
  • Beynon J. H.
  • Sellars C. M.
  , 2000. No abstract provided
• Caractérisation morphologique 3D des matériaux de structure hétérogènes par microtomographie X et traitement d'image pour la prévision du comportement mécanique
  
  • Bornert Michel
  • Jeulin Dominique
  • Maire E.
  • Moulinec H.
  • Chaix J.-M.
  , 2000. No abstract provided
• Etude expérimentale du comportement à la fissuration des dépôts de tungstène PVD en fonction de leurs épaisseurs
  
  • Ganne T.
  • Crépin Jérôme
  • Zaoui A.
  • Pradeilles-Duval R. M.
  , 2000. No abstract provided
• Finite element simulation of the deformation of b.c.c. aggregates using a crystal plasticity model - local orientation effects
  
  • Arizmendi D.
  • Raphanel J. L.
  , 2000, pp.27-32. No abstract provided
• Full or partial geometrical symmetry in symmetric Galerkin BEM
  
  • Bonnet Marc
  , 2000, pp.57-62. No abstract provided
• Folding and localized faulting in a frictional, cohesive overburden resting over a viscous substratum
  
  • Leroy Y.M.
  • Triantafyllidis N.
  , 2000, pp.109-140.
• Principles for the `intelligent' optimal design of materials and structures
  
  • Zarka Joseph
  , 2000.
• Crack propagation from a pre-existing flaw at a notch root. II: Detailed form of the stress intensity factors at the initial crack tip and conclusion
  
  • Leblond Jean-Baptiste
  • Mouro Pierre
  International Journal of Fracture, Springer Verlag, 2000, 104, pp.225-239. This paper pursues the study of crack kinking from a pre-existing crack emanating from some notch root. It was shown in Part I that the stress intensity factors at the tip of the small initial crack are given by universal (that is, applicable in all situations, whatever the geometry of the body and the loading) formulae; they depend only on the `stress intensity factor of the notch' (the multiplicative coefficient of the singular stress field near the apex of the notch in the absence of the crack), the length of the crack, the aperture angle of the notch and the angle between its bisecting line and the direction of the crack. Here we identify the universal functions of the two angles just mentioned which appear in these formulae, by considering the model problem of an infinite body endowed with a notch with straight boundaries and a straight crack of unit length. The treatment uses Muskhelishvili's complex potentials formalism combined with some conformal mapping. The solution is expressed in the form of an infinite series involving an integral operator, which is evaluated numerically. Application of Goldstein and Salganik's principle of local symmetry then leads to prediction of the kink angle of the crack extension. It is found that although the direction of the crack is closer to that of the bisecting line of the notch after kinking than before it, the kink angle is not large enough for the crack tip to get closer to this line after kinking, except perhaps in some special situations. (10.1023/A:1007637416241)
  DOI : 10.1023/A:1007637416241
• Évaluation de la biodisponibilité des dermocorticoïdes par thermographie infrarouge différentielle
  
  • Luong Minh Son
  • Luong Minh-Phong
  • Lok Catherine
  • Carmi Esther
  • Chaby Guillaume
  • Viseux Valérie
  Annales de Dermatologie et de Vénéréologie, Elsevier Masson, 2000, 127 (8-9), pp.701-705. Introduction</br> La technique thermographique infrarouge différentielle utilise le rayonnement infrarouge émis par la peau pour détecter, de façon non invasive et sans contact, les températures et leurs variations. Elle permet ainsi d'analyser les propriétés pharmacodynamiques (vasoconstriction) des dermocorticoïdes.</br></br> Matériels et méthodes</br> La carte thermique (thermogramme) cutanée a été enregistrée en temps réel à l'aide d'un système de détection de rayonnement infrarouge. Un test d'application unique sur un temps court, sans occlusion, et un test classique de blanchiment cutané après occlusion ont été réalisés. Un traitement par soustraction d'images a facilité l'analyse thermographique de l'effet des dermocorticoïdes des quatre classes d'activité sur peau saine.</br></br> Résultats</br> Nos résultats montrent, après une application unique sur un temps court, sans occlusion, des différences de température dans les 3 premières heures selon les corticoïdes. Le dermocorticoïde de classe II étudié en crème a provoqué un refroidissement plus intense que les autres dermocorticoïdes. L'effet de blanchiment cutané a été plus marqué pour les dermocorticoïdes de classe I et II et n'a pas été détecté pour celui de la classe IV.</br></br> Discussion</br> La possibilité de soustraire les thermogrammes les uns des autres permet d'exploiter le concept de différentielle d'images. Des différences évolutives de température après application unique, sans occlusion, de dermocorticoïdes sont mises en évidence dès les 3 premières heures. Ceci pourrait correspondre à des différences de puissance alors que le test classique de vasoconstriction n'étudie la blancheur cutanée induite qu'à partir de la 6 e heure. Pour le test de blanchiment cutané, les résultats de cette première étude sont insuffisants pour apporter une interprétation précise qualitative et quantitative. L'intérêt de la technique thermographique infrarouge différentielle est d'être une méthode quantitative, ne nécessitant pas de contact avec la peau, permettant un enregistrement continu en temps réel. Elle est plus sensible que la thermographie infrarouge classique. Elle a permis de réaliser une étude évolutive objective de l'action des dermocorticoïdes.
• Second-order and affine estimates for the behaviour of viscous polycrystals
  
  • Bornert Michel
  • Masson Renaud
  • Ponte-Castañeda P.
  Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, Wiley-VCH Verlag, 2000, 80, pp.S17-S20. The recently proposed second‐order and affine estimates for the effective behavior of nonlinear heterogeneous materials rely on the same linearization procedure and refer to some “thermoelastic comparison composite”. But both approaches differ in the way the overall nonlinear answer is defined, either through average stress‐strain relations or energy considerations. When combined with the linear self‐consistent model, they provide new tools for the predictions of the behavior of viscoplastic polycrystals (steady state creep). They are compared to each other and to other more classical estimates (incremental and tangent) in the following situations.: a 2D antiplane model problem for which efficient rigorous upper bounds are available, the creep of isotropic aggregates of FCC crystals and HCP crystals with different critical stresses on the basal and prismatic slip systems. (10.1002/zamm.20000801305)
  DOI : 10.1002/zamm.20000801305
• Stability and Nonlinear Solid Mechanics
  
  • Nguyen Quoc Son
  , 2000, pp.416 pages. Although the problem of stability and bifurcation is well understood in Mechanics, very few treatises have been devoted to stability and bifurcation analysis in dissipative media, in particular with regard to present and fundamental problems in Solid Mechanics such as plasticity, fracture and contact mechanics. Stability and Nonlinear Solid Mechanics addresses this lack of material, and proposes to the reader not only a unified presentation of nonlinear problems in Solid Mechanics, but also a complete and unitary analysis on stability and bifurcation problems arising within this framework. Main themes inlude : . elasticity and plasticity problems in small and finite deformation . general concepts of stability and bifurcation and basic results . elastic buckling . plastic buckling of structures . standard dissipative systems obeying maximum dissipation. These themes are developped in 20 chapters and illustrated by various analytical and numerical results. The coverage given here extends beyond the limited boundaries of previous works, resulting in a text of lasting interest and value to postgraduate students, researchers and practitioners working in mechanical, civil and aerospace engineering, as well as materials science.
• Behaviour characterisations of sheet metals, metallic honeycombs and foams at high and medium strain rates
  
  • Zhao H.
  • Gary G.
  Key Engineering Materials, Trans Tech Publications, 2000, 177-180, pp.225-230. This paper deals with dynamic testing and modelling of the metallic materials and soft structural material made of metals such aluminium honeycombs and foams. Tests are performed with the SHPB (Split Hopkinson Pressure Bar) system which is frequently used in a range of strain rates which correspond to those involved in most of civil industrial applications. Improvements of the SHPB were necessary in order to obtain reliable results on soft structural materials. Some experimental results and their modelling for metals as well as for aluminium honeycombs and foams wil1 be presented. (10.4028/www.scientific.net/KEM.177-180.225)
  DOI : 10.4028/www.scientific.net/KEM.177-180.225
• Effets d'un préécrouissage ou d'un surécrouissage cyclique sur la durée de vie en fatigue de divers aciers, à contrainte ou déformation imposée.
  
  • Doquet Véronique
  • Taheri Said
  Revue Française de Mécanique, 2000, 1, pp.27-33.
• Study of the mechanical behaviour of plasma deposited silica films on polycarbonates and steel
  
  • Hofrichter Alfred
  • Constantinescu Andrei
  • Benayoun Stéphane
  • Bulkin Pavel
  • Drévillon Bernard
  Journal of Vacuum Science & Technology A, American Vacuum Society, 2000, 18, pp.2012-2014. In the present study, we deposited amorphous hydrogenated silicon oxide films on polycarbonate, stainless steel, and silicon by plasma enhanced chemical vapor deposition using a low pressure, high density integrated distributed electron cyclotron resonance plasma reactor. Substrate curvature, vibrating slab, and Vickers indentation experiments were used to evaluate the intrinsic stress, the Young modulus of the films, and the composite hardness of the film–substrate system. The indentation experiments were modeled by finite element analysis and the calculated values were compared to experimentally measured hardness values. A reasonable accordance with the experiment was found both for stainless-steel and polycarbonate substrates, indicating that the modeling is valid and may be used to enhance the interpretation of the indentation experiments. The calculations show an important bending of the film in the noncontact region in the case of a Vickers indentation on a coated polycarbonate sample. The analysis of the thus-induced strain distribution in the coating indicates that the measured diagonal might be overestimated and not representative of the real contact area. The calculations indicate that the yield limit of the plasma-deposited silica films is of about 4 GPa. (10.1116/1.582464)
  DOI : 10.1116/1.582464
• An inverse approach to determine the non-linear properties of induction heat-treated steels
  
  • Niclas André
  • Bourgeois Lament
  European Journal of Mechanics - A/Solids, Elsevier, 2000, 19, pp.69-88. The identification of the through-the-thickness variation of the non-linear properties of a steel structure due to a heat treatment by induction is considered. An inverse approach to that problem is proposed, which is based on a 4-point bending test of a heat-treated parallelepipedic bar. It includes a layer-removal method for measuring residual stresses. Precisely, two different inverse methods are described. For a medium carbon steel, an application based on experimental data is performed, which shows the efficiency of our approach and a good agreement between the two methods. (10.1016/S0997-7538(00)00152-2)
  DOI : 10.1016/S0997-7538(00)00152-2
• Stabilité et Mécanique Non linéaire
  
  • Nguyen Quoc Son
  , 2000, pp.461 pages. Stabilité et mécanique non linéaire présente deux aspects fondamentaux de la mécanique non linéaire des solides : l'analyse de réponse statique et l'analyse de stabilité des matériaux et des structures. Il s'agit d'une approche synthétique des notions de base et des principaux résultats concernant l'évolution quasi-statique, la stabilité et la bifurcation des systèmes réversibles ou dissipatifs usuels. Elle concerne par exemple les solides élastiques, élasto-plastiques ou visco-plastiques en petite ou en grande transformation, ces solides étant soumis à des chergements mixtes classiques ou à des conditions de contact unilatéral avec frottement, ou comportant des propagations de fissures internes. L'ouvrage présente les derniers développements de la modélisation des solides en liaison avec les apports de la thermodynamique et de l'analyse convexe. Bon nombre de ces résultats sont issus des travaux de recherche récents du Laboratoire de Mécanique des Solides de l'Ecole Polytechnique. il s'adresse plus particulièrement aux enseignants, aux chercheurs, aux ingénieurs et lecteurs avertis cherchant une approche variationnelle privilégiant l'esprit mécanique. Il fait le lien entre les ouvrages de mécanique de style classique et les traités mathématiques peu adaptés au contexte de la mécanique des solides. Quoc Son Nguyen est directeur de recherche au CNRS et auteur d'une centaine de publications scientifiques. Ses travaux au sein du Laboratoire de Mécanique des Solides (Ecole Polytechnique) portent essentiellement sur la plasticité, la rupture et la stabilité.