Publications

2006

• High-strain Rate Tensile Testing Using a Split Hopkinson Pressure Bar
  
  • Mohr Dirk
  • Gary Gérard
  Journal de Physique IV Proceedings, EDP Sciences, 2006, 134, pp.617-622. A specially-designed specimen is proposed to investigate the tensile response of metals at high strain rates. This specimen may be directly used in a conventional split Hopkinson pressure bar system, thereby overcoming difficulties related to the gripping of traditional tensile specimens in dynamic testing. The specimen geometry has been optimized using finite element analysis. The dominant stress state in the specimen gage section is transverse plane strain. Explicit expressions are given to obtain the equivalent uniaxial stress-strain curve from the force and displacement measurements at the specimen boundaries. Quasi-static experiments have been carried and compared with standard uniaxial tensile tests to evaluate the accuracy of the force-stress and displacement-strain relationships. Using this new specimen, dynamic experiments have been performed on aluminum 2024-T351 showing that strain rates in the range of 1000/s may be obtained without oscillations. (10.1051/jp4:2006134095)
  DOI : 10.1051/jp4:2006134095
• Tribological and corrosion experiments of graphite ring against Ti-6Al-4V disk: Influence of electrochemical and mechanical parameters
  
  • Serre Ingrid
  • Pradeilles-Duval Rachel Marie
  • Celati N.
  Wear, Elsevier, 2006, 260, pp.1129-1135. Friction of two materials in artificial seawater induces severe degradations of both antagonists. In view of evaluating materials wear resistance, this investigation is devoted to the development of a new ring-on-disk tribocorrosimeter device. Its relevance to the study of wear due to plan/plan friction is analyzed comparing it to classical pin-on-disk experiments, with special emphasis on the influence of several factors: choice and respective position of both materials in contact, applied load, test duration. (10.1016/j.wear.2005.07.007)
  DOI : 10.1016/j.wear.2005.07.007
• Numerical and experimental study of the dynamic behaviour of Cork
  
  • Gameiro Celina Pires
  • Cirne José
  • Gary Gérard
  • Miranda Victor
  • Pinho-Da-Cruz Joaquim
  • Teixeira-Dias Filipe
  , 2005, pp.65-84. Cork is a natural cellular material with increasing industry applications due to its remarkable combination of properties. Its mechanical behaviour explains why it is often used for applications like sealing, packaging, insulation, vibration control, weight reduction, flotation, sound dampening and many others. However, the mechanical behaviour of cork when subjected to impact has not been well investigated yet. In the present work, the authors compare the quasi-static and dynamic response of four types of cork when compressed axially at strain rates from 10−3 s−1 to 600 s−1. Furthermore, in order to analyse the possible benefits to use the different types of cork in lightweight absorbing-energy structures, aluminum cork-filled tubes and their empty counterparts are tested experimentally and numerically at some quasi-static and dynamic strain rates under axial compressive loading. Data from the Split-Hopkinson Pressure Bar are used to generate stress-strain curves for natural and agglomerate cork samples. The numerical simulations of the dynamic compression of the specimens are performed using the finite element method software LS-DYNATM and show quite good agreement with the experimental results. In order to investigate the possible advantages of corkfilling in longer tubes with a different section, the authors also simulate the influence of the introduction of agglomerate cork in square aluminum tubes. For the cork-filled structures, when compared with the empty aluminum tubes, greater crushing forces and energy absorption capacities are observed (experimentally and numerically) for high values of the strain. The square structures analysed numerically, when filled with cork, show greater values of energy absorption since the beginning of the deformation process.
• Introduction à la diffraction inverse en acoustique et élasticité
  
  • Lambert Marc
  • Bonnet Marc
  • Lesselier Dominique
  , 2006, pp.82-101. Ce chapitre d'introduction aux problèmes inverses des ondes (acoustiques, élastiques) ne se veut pas une présentation exhaustive de leurs difficultés théoriques et numériques ni de leurs solutions en oeuvre dans les multiples champs applicatifs d'intérêt (dont ceux de l'évaluation et du contrôle non destructif de structures artificielles ou de la caractérisation du corps humain, deux sujets importants parmi ceux traités en profondeur dans d'autres chapitres du présent livre). Nous souhaitons seulement mettre en avant des éléments généraux, éléments que l'on imagine pouvoir être retrouvés de manière pertinente dans nombre de problèmes inverses effectivement affrontés. Peut-être plus encore, nous souhaitons aussi signaler au lecteur intéressé des pistes de réflexion ou de recherche, le tout en s'appuyant pour ce faire sur une poignée de publications de la littérature internationale récente, en donnant en sus en exemple des travaux auxquels les auteurs contribuent en identification topologique acoustique et élastique, investigation que nous croyons révélatrice à ce propos.
• A comparison of lifetime prediction methods for a thermal fatigue experiment
  
  • Amiable Sébastien
  • Chapuliot Stéphane
  • Constantinescu Andreï
  • Fissolo Antoine
  International Journal of Fatigue, Elsevier, 2006, 28, pp.692-706. This paper is dedicated to the comparison of several numerical models for estimating the lifetime in a fatigue experiment. The models simulate the SPLASH experiment, which produces thermal fatigue by locally quenching stainless steel specimens. All models predict first a stabilized mechanical state (plastic shakedown) and then a lifetime prediction using several fatigue crack initiation criteria. The numerical methods are either completely nonlinear or combine approximate elastic solutions obtained from minimizing a potential energy or closed form solutions with a Neuber or Zarka technique to estimate directly the elastoplastic state. The fatigue criteria used are Manson, dissipated energy and dissipated energy combined with a hydrostatic pressure term. The latter had provided a best prediction over a series of anisothermal and isothermal LCF experiments in a classical fatigue analysis. The analysis shows that for fatigue criteria taking into account the triaxiality of the mechanical response we obtain a systematic and conservative error. As a consequence of this work, we show that simplified models can be used for lifetime prediction. Moreover the paper provides a general technique to asses from the point of view of the design engineer the combination between a numerical method and a fatigue criterion. (10.1016/j.ijfatigue.2005.09.002)
  DOI : 10.1016/j.ijfatigue.2005.09.002
• Dynamic crushing behaviour of aluminium tubes filled with cork
  
  • Gameiro C.P.
  • Cirne J.
  • Gary Gérard
  Journal de Physique IV Proceedings, EDP Sciences, 2006, 134, pp.1207-1214. Cork is a natural cellular material with unique remarkable properties such as low density, great elasticity, chemical stability and resilience, no permeability to liquid and gases and resistance to wear and fire. Besides, it is ecological, hygienic, easy to maintain and a very durable material. Unfortunately, there are still application fields that have not been explored yet for the use of cork, possibly due to the fact that it is a complex cellular material, characterized by very variable mechanical properties which clearly depend on its microstructure. The fundamental aspects of the static and dynamic mechanical behaviour of natural and agglomerate cork, used alone and as filler inside a tube with small dimensions, under axial compressive loading, have already been studied by the authors. Aluminium cork-filled tubes and their empty counterparts were tested experimentally and numerically at quasi-static and dynamic strain rates from 10 - 3s - 1 to 600 s - 1. Data from the Split-Hopkinson Pressure Bar and “deconvolution” techniques were used to generate stress-strain curves for the structures composed of natural and agglomerate cork. The numerical simulations of the dynamic compression of the specimens were carried out using the finite element method software LS-DYNA$^{\rm TM}$ and showed quite good agreement with the experimental results. Hence, in this work, in order to extend the study started previously and investigate the possible advantages of cork-filling in longer tubes with a different section, the authors simulate, using the same software, the influence of the introduction of agglomerate cork in square and circular aluminium tubes with a diameter/width of 80 mm, a length of 300mm and a variable thickness. The mechanical properties of the structures composed of cork may constitute a potential for this material to be used in innovative applications related to diverse fields such as automotive, transport, ships and military applications. (10.1051/jp4:2006134184)
  DOI : 10.1051/jp4:2006134184
• On the overall behavior, microstructure evolution, and macroscopic stability in reinforced rubbers at large deformations: I-Theory
  
  • Lopez-Pamies Oscar
  • Ponte Castañeda Pedro
  Journal of the Mechanics and Physics of Solids, Elsevier, 2006, 54 (4), pp.807-830. This work presents an analytical framework for determining the overall constitutive response of elastomers that are reinforced by rigid or compliant fibers, and are subjected to finite deformations. The framework accounts for the evolution of the underlying microstructure, including particle rotation, which results from the finite changes in geometry that are induced by the applied loading. In turn, the evolution of the microstructure can have a significant geometric softening (or hardening) effect on the overall response, leading to the possible development of macroscopic instabilities through loss of strong ellipticity of the homogenized incremental moduli. The theory is based on a recently developed “second-order” homogenization method, which makes use of information on both the first and second moments of the fields in a suitably chosen “linear comparison composite,” and generates fairly explicit estimates—linearizing properly—for the large-deformation effective response of the reinforced elastomers. More specific applications of the results developed in this paper will be presented in Part II. (10.1016/j.jmps.2005.10.006)
  DOI : 10.1016/j.jmps.2005.10.006
• Identification d'obstacles en acoustique dans des domaines tridimensionnels bornés
  
  • Nemitz Nicolas
  • Bonnet Marc
  Revue Européenne de Mécanique Numérique/European Journal of Computational Mechanics, Hermès / Paris : Lavoisier, 2006, 15, pp.307-318. Cette communication concerne l'identification d'obstacles dans un domaine acoustique tridimensionnel borné. L'approche présentée repose sur deux ingrédients essentiels. Le premier est l'utilisation d'une méthode d'équations intégrales rapide fondée sur la fast multi-pole method, grâce à laquelle il est possible d'aborder ce type de problème d'inversion sur des configurations tridimensionnelles bornées de longueurs caractéristiques relativement grandes par rapport à la longueur d'onde acoustique. Le second est le gradient topologique de la fonction coût associée au problème inverse, permettant de déterminer les zones du domaine acoustique dans lesquelles l'introduction virtuelle d'un obstacle infinitésimal induit une diminution de la fonction coût. Cela permet par exemple de guider le choix de conditions initiales pour la mise en œuvre ultérieure d'un algorithme d'inversion reposant sur l'optimisation de la fonction coût. Ces deux aspects sont présentés et illustrés sur des exemples numériques. (10.3166/remn.15.307-318)
  DOI : 10.3166/remn.15.307-318
• Second-order theory for nonlinear composites and application to isotropic constituents
  
  • Idiart Martín I
  • Danas Kostas
  • Ponte Castañeda Pedro
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2006, 334 (10), pp.575-581. New prescriptions are proposed for the ‘reference’ fields in the context of the ‘second-order’ nonlinear homogenization method [P. Ponte Castañeda, Second-order homogenization estimates for nonlinear composites incorporating field fluctuations: I—Theory, J. Mech. Phys. Solids 50 (2002) 737–757], and are used to generate estimates for the effective behavior and first moments of the local fields in nonlinear composites. The new prescriptions yield simple, analytical expressions not only for the effective potentials, but also for the macroscopic stress-strain relation, as well as for the phase averages of the strain and stress fields. For illustrative purposes, ‘second-order’ estimates of the Hashin–Shtrikman type are provided for two-phase, transversely-isotropic composites with power-law phases, and are compared with exact results available for power-law, multiple-rank, sequential laminates. The agreement is found to be quite good for all ranges of nonlinearities and inclusion concentrations considered. (10.1016/j.crme.2006.06.006)
  DOI : 10.1016/j.crme.2006.06.006
• A computational lifetime prediction of a thermal shock experiment. Part II: discussion on difference fatigue criteria
  
  • Amiable Sébastien
  • Chapuliot Sébastien
  • Constantinescu Andreï
  • Fissolo Antoine
  Fatigue and Fracture of Engineering Materials and Structures, Wiley-Blackwell, 2006, 29, pp.219-228. The SPLASH experiment has been designed in 1985 by the CEA to simulate thermal fatigue due to cooling shocks on steel specimens and is similar to the device reported by Marsh in Ref. [1]. The purpose of this paper is to discuss the application of different fatigue criteria in this case. The fatigue criteria: dissipated energy, Manson Coffin, Park and Nelson, dissipated energy with a pressure term, are determined for the experiment using results from FEM computations presented in the first part of the paper (Part I) and compared with results from uniaxial and multiaxial experiments from literature. The work emphasizes the evolution of the triaxiality ratio during the loading cycle. (10.1111/j.1460-2695.2006.0983.x)
  DOI : 10.1111/j.1460-2695.2006.0983.x
• Identification of poroelastic constants of tight rocks from laboratory tests
  
  • Lecampion Brice
  • Constantinescu Andrei
  • Malinski Laurent
  International Journal of Geomechanics, American Society of Civil Engineers, 2006, 6, pp.201-208. This paper discusses the identification of poroelastic constants and hydraulic conductivity from two transient laboratory tests performed on cylindrical core: drained isotropic confinement and pulse test. The combination of the two tests allows us to estimate all poroelastic parameters with the exception of the shear modulus. Despite the lack of analytical solutions for the fully coupled case, closed form solutions of the forward problems are obtained for a slender specimen. The validity of these solutions for a realistic aspect ratio of the core is assessed by a comparison with a finite element model. The identification problem is solved by minimizing a least square functional using an explicit gradient computed using the direct differentiation of the closed form solution and a Levenberg–Marquardt algorithm. The uniqueness of this inverse problem as well as the effect of noise on input data are fully discussed. The identification procedure is then applied to tests performed on a deep argillaceous rock (argillite of Meuse Haute–Marne). (10.1061/(ASCE)1532-3641(2006)6:3(201))
  DOI : 10.1061/(ASCE)1532-3641(2006)6:3(201)
• Extensométrie surfacique et volumique pour l'analyse multi-échelle des matériaux
  
  • Bornert Michel
  , 2006.
• Localisation dans les milieux poreux linéaires fortement anisotropes
  
  • Willot François
  • Pellegrini Yves-Patrick
  • Castañeda Pedro Ponte
  • Idiart Martin
  , 2006.
• Small-obstacle expansion for 3D acoustic and elastodynamic inverse scattering
  
  • Bonnet Marc
  , 2006. (10.1088/0266-5611/24/3/035022)
  DOI : 10.1088/0266-5611/24/3/035022
• Topological sensitivity and FMM-accelerated BEM applied to 3D acoustic inverse scattering
  
  • Nemitz Nicolas
  • Bonnet Marc
  , 2006. This study is set in the framework of inverse scattering of scalar (e.g. acoustic) waves. A qualitative probing technique based on the distribution of topological sensitivity of the cost functional associated with the inverse problem with respect to the nucleation of an infinitesimally small hard obstacle is formulated. The sensitivity distribution is expressed as a bilinear formula involving the free field and an adjoint field associated with the cost function. These fields are computed by means of a boundary element formulation accelerated by the fast multipole method. A computationally fast approach for performing a global preliminary search based on the available overspecified boundary data is thus defined. Its usefulness is demonstrated through results of numerical experiments on the qualitative identification of hard obstacles in a bounded 3D acoustic domain, for configurations featuring nodal unknowns and sampling points, based on exact or noisy synthetic data. (10.1016/j.enganabound.2007.02.006)
  DOI : 10.1016/j.enganabound.2007.02.006
• TGV disc brake squeal
  
  • Lorang Xavier
  • Foy-Margiocchi Florence
  • Son Nguyen Quoc
  • Gautier Pierre-Etienne
  Journal of Sound and Vibration, Elsevier, 2006, 293, pp.735-746. The discomfort generated by the noise emission of braking systems in train has aroused recently many studies on the mechanical modeling of brake noise in France. A theoretical and numerical discussion on the phenomenon of brake squeal is given here in relation with some experimental data. This study is based upon a flutter instability analysis giving the unstable modes of the TGV brake system. (10.1016/j.jsv.2005.12.006)
  DOI : 10.1016/j.jsv.2005.12.006
• Work of indentation approach to the analysis of hardness and modulus of thin coatings
  
  • Korsunsky Alexander
  • Constantinescu Andreï
  Materials Science and Engineering: A, Elsevier, 2006, 423, pp.28-35. The problem of accurate identification of mechanical properties, primarily hardness and modulus, invariably arises whenever very thin coatings are considered that consist of single or multiple layers, e.g. in the context of fitness-for-purpose characterisation of coated systems, monitoring in-service degradation, component lifetime prediction, etc. Rapid developments in the areas of nano-fabrication, nano-manipulation and nano-technology lead to the increased importance of reliable characterisation of mechanical properties of progressively thinner coatings. Instrumented small scale (nano-) indentation is particularly well-suited to surface-engineered and thin-coated systems. The present study presents a review and refinement of the interpretation techniques for instrumented (nano) indentation for reliable property de-convolution of coated systems. Particular attention is devoted to contact modulus and hardness, as the properties that play the key role in controlling the deformation response of any surface, and affect such service properties as impact and erosion resistance, wear and fretting fatigue resistance, resistance to crack initiation and propagation, etc. A flexible multi-scaling power law functional description is introduced and discussed, and its application to various example systems is illustrated. (10.1016/j.msea.2005.09.126)
  DOI : 10.1016/j.msea.2005.09.126
• Min-max Duality and Shakedown Theorems in Plasticity
  
  • Nguyen Quoc Son
  , 2006, pp.81-92. This paper gives an overall presentation of shakedown theorems in perfect and in hardening plasticity. General results on shakedown theorems are discussed in the framework of generalized standard materials. The starting point is a static shakedown theorem available for perfect and for hardening plasticity. It leads by min-max duality to the dual static and kinematic approaches to compute the safety coefficient with respect to shakedown. These approaches are discussed for common models of isotropic and of kinematic hardening. In particular, the kinematic approach leads to some new results on the expressions of the safety coefficient. (10.1000/ISBN-0387291962)
  DOI : 10.1000/ISBN-0387291962
• Écart à la réciprocité et identification de fissures en thermoélasticité isotrope transitoire
  
  • Andrieux Stéphane
  • Bui Huy Duong
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2006, 334, pp.225-229. On s'intéresse à un solide élastique isotrope renfermant une ou plusieurs fissures planes, et soumis à un chargement d'origine thermique variable dans le temps. On relève la valeur du champ de déplacement et du champ des tractions surfaciques sur le bord du solide. On propose dans cette Note la définition et l'exploitation d'un écart à la réciprocité, formulé uniquement à partir des grandeurs mécaniques connues sur le bord du solide, qui permet de déterminer explicitement le plan renfermant la ou les fissures, les conditions régnant sur celles-ci étant quelconques dès lors qu'elles assurent la continuité du vecteur contrainte et du flux de chaleur normal. (10.1016/j.crme.2006.02.004)
  DOI : 10.1016/j.crme.2006.02.004
• Rheology of the lower crust: laboratory data and field observations,
  
  • Dresen Georg
  • Dimanov A.
  • Rybacki E.
  • Xiaohui X.
  • Kenkmann T.
  • Wirth R.
  , 2006.
• A direct method for the solution of evolution problems
  
  • Comte François
  • Maitournam M.
  • Burry Pierre
  • Nguyen T. Mac Lan
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2006, 334 (5), pp.317-322. An alternative numerical method to solve structural evolution problems is presented. It belongs to the family of Large Time Increment Methods. The problem is solved on the whole time interval separating a global stage where a SA and KA solution is searched and a local stage where the constitutive law is satisfied. To solve the global stage, consuming the most CPU time, the mechanical fields are decomposed in a wavelet basis and the equilibrium is solved only for the largest coefficients. (10.1016/j.crme.2006.02.007)
  DOI : 10.1016/j.crme.2006.02.007
• An integral-equation approach for small-obstacle approximation in 3D acoustic and elastodynamic inverse scattering
  
  • Bonnet Marc
  , 2006.
• Influence de la morphologie microstructurale sur la réponse mécanique de polycristaux biphasés
  
  • Rupin N.
  • Bornert Michel
  • Zaoui A.
  • Pinna C.
  • Gilormini P.
  , 2006.
• Multi-scale finite-strain plasticity model for stable metallic honeycombs incorporating microstructural evolution
  
  • Mohr Dirk
  International Journal of Plasticity, Elsevier, 2006, 22, pp.1899-1923. This paper deals with the development of a mechanism-based two-scale constitutive model for thick-walled metallic honeycombs in sandwich applications. The mechanical response of metallic honeycomb sandwich sheets subject to large in-plane normal loading and out-of-plane shear loading is investigated using a detailed finite element model of the honeycomb microstructure. Based on the simulation results, a simple micro-mechanical system is proposed and used to develop the macroscopic constitutive model. The finite-strain constitutive model accounts for microstructural evolution due to geometrical changes and strain hardening at the microscale. The macroscopic model has been validated for various loading conditions. Furthermore, the evolution of the macroscopic yield surface for pure out-of-plane shear is discussed in detail. (10.1016/j.ijplas.2006.01.004)
  DOI : 10.1016/j.ijplas.2006.01.004
• Modélisation numérique du Friction Stir Welding
  
  • Bastier Arnaud
  • Maitournam Habibou
  • Dang Van Ky
  • Roger Frédéric
  Revue Européenne de Mécanique Numérique/European Journal of Computational Mechanics, Hermès / Paris : Lavoisier, 2006, 15, pp.41-52. Le travail présenté dans cet article décrit une méthode de calcul destinée à la simulation d’un procédé de soudage appelé Friction Stir Welding. À partir d’une loi de comportement viscoplastique et d’une approche eulérienne, le champ de température est évalué en tenant compte de l’écoulement de matière autour de l’outil. Ce premier résultat, obtenu à l’aide d’une résolution par éléments finis mixtes, est validé par des données expérimentales issues de measures obtenues par thermographie infrarouge. La seconde étape du calcul a pour but de determiner les contraintes résiduelles de l’assemblage après soudage. Pour cela, un algorithme élastoplastique stationnaire est utilisé. Lors du calcul, l’histoire mécanique de la matière est prise en compte en intégrant le comportement le long des trajectoires suivies par les points matériels. Seule la phase stationnaire du procédé sera simulée dans l’ensemble de ce travail. (10.3166/remn.15.41-52)
  DOI : 10.3166/remn.15.41-52