Publications

2008

• Autoéchauffement, fatigue thermomécanique des élastomères
  
  • Le Chenadec Yohan
  , 2008. Les élévations de température à proximité des pièces en élastomères automobiles rendent insuffisantes les méthodes expérimentales actuellement utilisées pour dimensionner ces pièces. Ainsi, il est essentiel de mettre au point une nouvelle approche, tant expérimentale que numérique, permettant d'estimer la durée de vie d'une structure en élastomère soumise à la fois à une histoire de chargement thermique et de chargement mécanique. Le matériau d'étude est un caoutchouc naturel chargé au noir de carbone. Ce matériau présente deux caractéristiques importantes à prendre en compte dans le cadre de cette étude. D'une part, en raison de son comportement hystérétique, il a la propriété de s'échauffer sous l'effet d'une sollicitation mécanique ; ainsi la température du matériau ne dépend pas uniquement des conditions aux limites thermiques mais également mécaniques. D'autre part, sa tenue en endurance se dégrade notablement lorsque la température augmente. L'objectif du travail de thèse est de proposer des méthodes d'estimation de la durée de vie pour la fatigue thermomécanique des élastomères. Afin de répondre à cet objectif, nous caractérisons tout d'abord les histoires de chargement mécanique et thermique en tenant compte des couplages thermomécaniques. En particulier, nous étudions le comportement thermomécanique cyclique, et développons une méthode d'estimation simple et robuste de la température d'autoéchauffement. Cette méthode est fondée sur un couplage thermomécanique faible, une estimation des sources de chaleur et un problème thermique homogénéisé en temps incluant les effets des grandes déformations. Afin de bâtir un modèle de fatigue thermomécanique, nous caractérisons l'endurance du matériau d'étude à partir de courbes de Wöhler et de renforcement à plusieurs températures. Nous discutons de l'hypothèse de cumul linéaire d'endommagement par fatigue (règle de Miner) pour des sollicitations thermomécaniques.
• Modelling of the residual state of friction stir welded plates
  
  • Bastier A.
  • Maitournam Habibou
  • Roger F.
  • Dang Van K.
  Journal of Materials Processing Technology, Elsevier, 2008, 200 (1-3), pp.pp 25-37. This paper presents a steady-state simulation of friction stir welding based on a prior computational method developed in [Bastier, A., Maitournam, M.H., Dang Van, K., Roger, F., 2006. Steady state thermomechanical modelling of friction stir welding. Sci. Technol. Weld. Joining 11 (3), 278–288]. This simulation includes two main steps. The first one uses an Eulerian description of the thermomechanical problem: a 3D-mixed Finite Element Model based on a Computational Fluid Dynamics package is used to establish the material flow and the temperature field during the process. In the second step, a steady-state algorithm based on an elastoviscoplastic constitutive law is used to estimate the residual state induced by the process. The steady-state assumption and the original elastoviscoplastic constitutive law are two key features of the present model. This calculation takes into account the whole thermal, metallurgical and mechanical history of the material since the algorithm is based on an integration along the path lines of the particles. The material considered is a 7050 aluminium alloy. It is observed that the longitudinal residual stress field has a two peaks profile: these two peaks are situated in the zone of high gradient of dissolved precipitates fraction. Finally, a parametric study about the influence of welding and rotational speeds is carried out. This parametric study shows that the higher the welding speed and the lower the rotational speed, the lower the temperatures and the lower residual distortions. (10.1016/j.jmatprotec.2007.10.083)
  DOI : 10.1016/j.jmatprotec.2007.10.083
• Heterogeneous materials with evolving microstructure : constitutive modeling, numerical implementation and applications.
  
  • Danas Konstantinos
  , 2008. Le travail de thµese porte sur l'application de la methode non-lineaire d' homogeneisation dite du second- ordre de Ponte Casta~neda (2002) pour estimer le comportement effectif des materiaux poreux viscoplastique. A titre de rappel, cette methode est basee sur la construction des principes variationnels appropries en utilisant un composite lineaire de comparaison pour produire des evaluations correspondantes µa des milieux poreux non-lineaires. Ainsi, l'objectif principal de ce travail est de proposer un modµele constitutif general qui tient compte de l' evolution de la microstructure, et par consequent, de l'anisotropie induite par l'application de deformations nies au materiau poreux. Le modele est construit pour reproduire exactement le comportement d'un assemblage de sphere composites dans la limite des chargements hydrostatiques, et concide donc avec la limite hydrostatique du critere de Gurson (1977) pour des materiaux poreux plastiques avec des microstructures isotropes. En consequence, ce nouveau modµele ameliore les estimations d'homogeneisation existantes, lesquelles sont satisfaisantes pour de faibles triaxialites mais excessivement raides pour des triaxialites et des non-linearites elevees. En outre, les estimations obtenues par le modµele dependent de la troisieme invariable du tenseur macroscopique des contraintes, lequel porte un effet non negligeable sur la reponse eective du materiau pour de moyennes et hautes triaxialites. De plus, les resultats cites ci-dessus ont ete generalises µa des microstructures anisotropes complexes (par exemple : des microstructures avec des formes et des orientations arbitraires des pores) et a des chargements tridimensionnels, conduisant a la reponse anisotrope globale du materiau poreux. Le modele est ensuite etendu pour tenir compte de l'evolution de la microstructure lorsque le materiau est soumis µa des deformations nies. Enn, la validation du modµele propose a ete realisee par le biais de calculs par elements ¯nis sur des mi-crostructures axisymetriques periodiques, et donnent des resultats pertinents pour l'ensemble des triaxialites et des non-linearites envisagees.
• A CRACKED BEAM FINITE ELEMENT FOR ROTATING SHAFT DYNAMICS AND STABILITY ANALYSIS
  
  • El Arem Saber
  • Maitournam Habibou
  Journal of Mechanics of Materials and Structures, Mathematical Sciences Publishers, 2008, 3 (5), pp.893-910. In this paper, a method for the construction of a cracked beam finite element is presented. The additional flexibility due to the cracks is identified from three-dimensional finite element calculations taking into account the unilateral contact conditions between the crack lips. Based on this flexibility, which is distributed over the entire length of the element, a cracked beam finite element stiffness matrix is deduced. Considerable gain in computing efforts is reached compared to the nodal representation of the cracked section when dealing with the numerical integration of differential equations in structural dynamics. The stability analysis of a cracked shaft is carried out using the Floquet theory. (10.2140/jomms.2008.3.893)
  DOI : 10.2140/jomms.2008.3.893
• Local approach to fatigue crack bifurcation
  
  • Doquet Véronique
  • Bertolino Graciela
  International Journal of Fatigue, Elsevier, 2008, 30 (5), pp.942-950. A “local approach” of bifurcation based on the application at the crack tip of two critical-plane fatigue criteria predicting either tensile-stress-dominated or shear-dominated fracture and on the choice of the fastest damage mode is proposed. In pure mode II, this approach is shown to successfully predict a transition from bifurcation, as predicted by usual criteria, to coplanar crack growth when DKII increases, which usual criteria fail to predict. It is also shown that the deceleration and final bifurcation of cracks propagating in shear-mode is not due to a stress/strain redistribution as the crack propagates through its plastic zone but can really be attributed to a friction-induced decrease in effective DKII. The proposed approach may also be used for unconstrained plasticity or non-proportional loading and it is sensitive to the loading path. An application to sequential mode I and II is presented. The synergy of mode I and mode II in that case is captured.
• Mesures de champs et identification de modèles de plasticité cristalline
  
  • Gérard Céline
  , 2008. L'identification des lois de comportement multi-échelles des matériaux polycristallins est étudiée. Une méthode couplant calculs par léments finis et modèles en champs moyens est développée. La description des interactions entre systèmes de glissement est améliorée par confrontation des réponses expérimentales et issues de la simulation du comportement d'un cuivre OFHC, sous chargements complexes. La localisation de la déformation est analysée grâce à des mesures de champs réalisées, sous microscope électronique à balayage. Une microstructure synthétique tridimensionnelle représentative est développée à partir des cartographies EBSD. Par ailleurs, on effectue la confrontation, sur microstructure périodique, entre plusieurs modèles en champs moyens et les simulations par éléments finis, à l'échelle des états moyens par phase. Le volume élémentaire représentatif est défini aux échelles globales et locales.
• New Trends in Scientific and Technical Information
  
  • Salençon Jean
  , 2008.
• Shakedown Theorems in Contact Mechanics
  
  • Antoni Nicolas
  • Nguyen Quoc Son
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2008, 336 (4), pp.341-346. In this paper, the phenomenon of cumulative slip of solids under cyclic load is considered. The topic concerns with the relative displacements of two solids maintained in contact by friction. The statement of Melan's theorem is first given under the assumption of full contact under Tresca friction. It suggests again the definition of a safety coefficient with respect to shakedown. The safety coefficient can be computed by static or kinematic approaches. For Coulomb friction, these general results do not hold. Numerical calculations by step by step integration show that the asymptotic behaviour with or without shakedown could be obtained very quickly, after some cycles. (10.1016/j.crme.2007.11.021)
  DOI : 10.1016/j.crme.2007.11.021
• Micro-macro characterization and modelling of human cortical bone : structural anisotropy versus material anisotropy.
  
  • Ho Ba Tho M.C.
  • Vanleene M.
  • Bensamoun S.F.
  • Stolz C.
  , 2008.
• Macroelement modeling of shallow foundations
  
  • Chatzigogos Charisis
  • Pecker Alain
  • Salençon J.
  , 2008. The paper presents a new macroelement model for shallow foundations. The model is defined through a non-linear constitutive law written in terms of some generalized force and displacement parameters. The linear part of this constitutive law comes from the dynamic impedances of the foundation. The non-linear part comprises two mechanisms. One is due to the irreversible elastoplastic soil behavior: it is described with a bounding surface hypoplastic model, adapted for the description of the cyclic soil response. An original feature of the formulation is that the bounding surface is considered independently of the surface of ultimate loads of the system. The second mechanism is the detachment that can take place at the soil-footing interface (foundation uplift). It is totally reversible and non-dissipative and can thus be described by a phenomenological non-linear elastic model. The macroelement is qualitatively validated by application to soil-structure interaction analyses of simple real structures.
• Analytical results for the plectonemic response of supercoiled DNA
  
  • Clauvelin Nicolas
  • Audoly Basile
  • Neukirch Sébastien
  Journal of Computer-Aided Materials Design, Springer Verlag, 2008, 14 (S1), pp.95-101. The DNA molecule is modeled as an elastic rod with bending and twisting rigidities, subjected to external tension and twist applied at one end, the other end being clamped. We study the plectonemic equilibrium of such a rod, taking into account the impenetrability constraint. Numerical solutions of this boundary value problem have previously shown that purely elastic models can reproduce the supercoiling response of the DNA molecule. Using a variational approach, we derive analytical formulae for the elastic response of the filament, and extend former numerical results. (10.1007/s10820-007-9072-y)
  DOI : 10.1007/s10820-007-9072-y
• A high-cycle fatigue life model for variable amplitude multiaxial loading
  
  • Jabbado M.
  • Maitournam Habibou
  Fatigue and Fracture of Engineering Materials and Structures, Wiley-Blackwell, 2008, 31 (1), pp.pp 67-75. A high-cycle fatigue life model for structures subjected to variable amplitude multiaxial loading is presented in this paper. It treats any kind of repeated blocks of variable amplitude multiaxial loading without using a cycle counting method. This model based on a mesoscopic approach is characterized by the following features: (i) the choice of a damage factor related to the accumulated mesoscopic plastic strain per stabilised cycle; (ii) the use of amesoscopicmechanical behaviour taking into account the fatigue mechanisms such as plasticity and void growth. This behaviour is a von Mises elastoplastic model with linear kinematic hardening and hydrostatic stress dependent yield stress. The fatigue life model has six parameters identified with one SN curve and two fatigue limits. In-phase and outof- phase experimental tests from the literature are simulated. The predicted fatigue lives are compared to experimental ones. (10.1111/j.1460-2695.2007.01201.x)
  DOI : 10.1111/j.1460-2695.2007.01201.x
• On the reconstruction of residual stresses after matter removal in rods
  
  • Constantinescu Andrei
  • Oueslati Abdelbacet
  Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, Elsevier, 2008, 336 (1-2), pp.66-79. This article discusses the reconstruction methods for the inversion of the residual stresses in rods under the Navier-Bernoulli or the Vlassov (containing warping) kinematic conditions. The proposed framework permits us to express the residual stresses in terms of the Airy stress potential expressed as the solution of an ordinary differential equation. The particular case of the Navier-Bernoulli kinematics leads to a closed-form solution. (10.1016/j.crme.2007.10.016)
  DOI : 10.1016/j.crme.2007.10.016
• Éléments d'acoustique linéaire
  
  • Boutillon Xavier
  , 2008.
• A homogenization-based constitutive model for isotropic viscoplastic porous media
  
  • Danas Kostas
  • Idiart Martin I.
  • Ponte Castañeda Pedro
  International Journal of Solids and Structures, Elsevier, 2008, 45, pp.3392-3409. An approximate model based on the "second-order" nonlinear homogenization method is proposed to estimate the effective behavior of isotropic, viscoplastic, porous materials. The model is constructed in such a way that it reproduces exactly the behavior of a "composite-sphere assemblage" in the limit of hydrostatic loadings, and therefore coincides with the hydrostatic limit of Gurson's criterion in the special case of ideal plasticity. As a consequence, the new model improves on earlier homogenization estimates, which have been found to be quite accurate for low triaxialities but overly stiff for sufficiently high triaxialities and nonlinearities. Additionally, the estimates delivered by the model exhibit a dependence on the third invariant of the macroscopic stress tensor, which has a nontrivial effect on the effective response of the material at moderate triaxialities. The proposed model is compared with exact results obtained for a special class of porous materials with sequentially laminated microstructures. The agreement is found to be quite good for the entire range of stress triaxialities, and all values of the porosity and nonlinearity considered. (10.1016/j.ijsolstr.2008.02.007)
  DOI : 10.1016/j.ijsolstr.2008.02.007
• Refined finite element modelling for the vibration analysis of large rotating machines
  
  • Combescure Didier
  • Lazarus Arnaud
  Journal of Sound and Vibration, Elsevier, 2008, 318. This paper is aimed at presenting refined finite element modelling used for dynamic analysis of large rotating machines. The first part shows an equivalence between several levels of modelling: firstly, models made of beam elements and rigid disc with gyroscopic coupling representing the position of the rotating shaft in an inertial frame; secondly full three-dimensional (3D) or 3D shell models of the rotor and the blades represented in the rotating frame and finally two-dimensional (2D) Fourier model for both rotor and stator. Simple cases are studied to better understand the results given by analysis performed using a rotating frame and the equivalence with the standard calculations with beam elements. Complete analysis of rotating machines can be performed with models in the frames best adapted for each part of the structure. The effects of several defects are analysed and compared with this approach. In the last part of the paper, the modelling approach is applied to the analysis of the large rotating shaft part of the power conversion unit of the GT-MHR nuclear reactor. (10.1016/j.jsv.2008.04.025)
  DOI : 10.1016/j.jsv.2008.04.025
• Intégrale duale en mécanique de la rupture.
  
  • Stolz Claude
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2008 (336), pp.434-439. We propose a dual approach in fracture mechanics based on complementary energy. The analysis of the dissipation shows that the thermodynamical force associated with the evolution of a crack is an energy release rate, form of which depends on the presence or not of mechanical discontinuities. This energy release rate is given as an integral based on free or complementary energy. We analyse the invariance of such integrals and we discuss the obtained results in elastoplasticity. Résumé On propose une intégrale duale en mécanique de la rupture ductile fondée sur l'énergie complémentaire. L'analyse de la dissipation mécanique en présence ou non de discontinuités mobiles montre que le paramètre énergétique associé à la vitesse de propagation est représenté par une intégrale de contour appropriée exprimée en terme d'énergie libre ou d'énergie complémentaire. On étudie alors l'invariance par rapport au contour de ces intégrales et on interpréte les résultats obtenus. (10.1016/j.crme.2008.02.002)
  DOI : 10.1016/j.crme.2008.02.002
• Comportement mécanique à très long terme des mines et cavernes dans le sel gemme : loi de Norton-Hoff ou loi de Lemaître ?
  
  • Berest Pierre
  • Bérest P.
  • Karimi-Jafari Mehdi
  • Brouard Benoît
  Revue française de Géotechnique, edp sciences, 2008 (124), pp.45-59.
• A multi-level fast-multipole multi-region method for 3-D frequency-domain elastodynamics
  
  • Chaillat Stéphanie
  • Semblat Jean-François
  • Bonnet Marc
  , 2008.
• Biaxial Testing of Sheet Materials at High Strain Rates Using Viscoelastic Bars
  
  • Grolleau Vincent
  • Gary Gérard
  • Mohr Dirk
  Experimental Mechanics, Society for Experimental Mechanics, 2008, 48 (3), pp.293-306. A dynamic bulge testing technique is developed to perform biaxial tests on metals at high strain rates. The main component of the dynamic testing device is a movable bulge cell which is directly mounted on the measuring end of the input bar of a conventional split Hopkinson pressure bar system. The input bar is used to apply and measure the bulging pressure. The experimental system is analyzed in detail and the measurement accuracy is discussed. It is found that bars made of low impedance materials must be used to achieve a satisfactory pressure measurement accuracy. A series of dynamic experiments is performed on aluminum 6111-T4 sheets using viscoelastic nylon bars to demonstrate the capabilities of the proposed experimental technique. The parameters of the rate-dependent Hollomon–Cowper–Symonds J2 plasticity model of the aluminum are determined using an inverse analysis method in conjunction with finite element simulations. (10.1007/s11340-007-9073-5)
  DOI : 10.1007/s11340-007-9073-5
• Interpretation of Mechanical Integrity Tests
  
  • Berest Pierre
  • Bérest P.
  , 2008, pp.1263-1270.
• L'effondrement de 1873 à la mine de Varangéville
  
  • Berest Pierre
  • Bérest P.
  , 2008, pp.281-288.
• Conception d'un algorithme de calcul du risque de chute de la personne âgée
  
  • Thibaud Marie
  • Bloch Frédéric
  • Brèque Cyril
  • Kemoun Gilles
  , 2008.
• MECHANICAL PROPERTIES OF GLENOID CANCELLOUS BONE
  
  • Kalouche Ibrahim
  • Abdelmoumen Samir
  • Crepin Jerome
  • Mitton David
  • Guillot Geneviève
  • Gagey Olivier
  Journal of Biomechanics, Elsevier, 2008, 41, pp.S 324.
• Theoretical and numerical modeling of solid-solid phase change: Application to the description of the thermodynamical behaviour of shape memory alloys
  
  • Moumni Ziad
  • Zaki Wael
  • Nguyen Quoc Son
  International Journal of Plasticity, Elsevier, 2008, 24 (xx), pp.614-645. The mechanical behaviour of a solid capable of undergoing internal phase change is considered. Reversible and dissipative constitutive equations are established within the framework of generalized standard materials with internal constraints. The constraints are accounted for using Lagrange multipliers. The presented model is based upon a phenomenological configuration in series (Reuss model). In the case of reversible phase change, it is shown that the elastic energy of the material can be obtained by convexification the energy functions of existing phases. In the dissipative case, it is shown how the behaviour of the material can be made stable by developing evolving equations from a suitable dissipation potential. As an application, a description of the thermomechanical behaviour of shape memory alloys (SMAs). The obtained constitutive equations can be used to simulate the pseudoelastic response of SMAs as well as the one-way shape memory effect. Validation against experimental data is performed in the case of multiaxial thermomechanical loading for NiTi and Cu-based alloys. (10.1016/j.ijplas.2007.07.007)
  DOI : 10.1016/j.ijplas.2007.07.007