Publications

2009

• Dual integrals in non linear fracture mechanics
  
  • Stolz Claude
  Vietnam Journal of Mechanics, Viện Hàn Lâm Khoa học và Công nghệ Việt Nam, 2009, 31 (3-4), pp.221-232.
• Damping efficiency of the Tchamwa–Wielgosz explicit dissipative scheme under instantaneous loading conditions
  
  • Mahéo Laurent
  • Grolleau Vincent
  • Rio Gérard
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2009, 337 (11-12), pp.722-732. To deal with dynamic and wave propagation problems, dissipative methods are often used to reduce the effects of the spurious oscillations induced by the spatial and time discretization procedures. Among the many dissipative methods available, the Tchamwa–Wielgosz (TW) explicit scheme is particularly useful because it damps out the spurious oscillations occurring in the highest frequency domain. The theoretical study performed here shows that the TW scheme is decentered to the right, and that the damping can be attributed to a nodal displacement perturbation. The FEM study carried out using instantaneous 1-D and 3-D compression loads shows that it is useful to display the damping versus the number of time steps in order to obtain a constant damping efficiency whatever the size of element used for the regular meshing. A study on the responses obtained with irregular meshes shows that the TW scheme is only slightly sensitive to the spatial discretization procedure used. (10.1016/j.crme.2009.10.005)
  DOI : 10.1016/j.crme.2009.10.005
• Infinite-contrast periodic composites with strongly nonlinear behavior: Effective-medium theory versus full-field simulations
  
  • Idiart Martin I.
  • Willot François
  • Pellegrini Yves-Patrick
  • Ponte Castañeda Pedro
  International Journal of Solids and Structures, Elsevier, 2009, 46 (18-19), pp.3365-3382. This paper presents a combined numerical-theoretical study of the macroscopic behavior and local field distributions in a special class of two-dimensional periodic composites with viscoplastic phases. The emphasis is on strongly nonlinear materials containing pores or rigid inclusions. Full-field numerical simulations are carried out using a Fast-Fourier Transform algorithm [H. Moulinec, P. Suquet, C. R. Acad. Sci. Paris II 318, 1417 (1994)], while the theoretical results are obtained by means of the `second-order' nonlinear homogenization method [P. Ponte Castaneda, J. Mech. Phys. Solids 50, 737 (2002)]. The effect of nonlinearity and inclusion concentration is investigated in the context of power-law (with strain-rate sensitivity m) behavior for the matrix phase under in-plane shear loadings. Overall, the `second-order' estimates are found to be in good agreement with the numerical simulations, with the best agreement for the rigidly reinforced materials. For the porous systems, as the nonlinearity increases (m decreases), the strain field is found to localize along shear bands passing through the voids (the strain fluctuations becoming unbounded) and the effective stress exhibits a singular behavior in the dilute limit. More specifically, for small porosities and fixed nonlinearity m>0, the effective stress decreases linearly with increasing porosity. However, for ideally plastic behavior (m = 0), the dependence on porosity becomes non-analytic. On the other hand, for rigidly-reinforced composites, the strain field adopts a tile pattern with bounded strain fluctuations, and no singular behavior is observed (to leading order) in the dilute limit. (10.1016/j.ijsolstr.2009.05.009)
  DOI : 10.1016/j.ijsolstr.2009.05.009
• Comparison of experimental results and finite element simulation of strain localization scheme under cyclic loading
  
  • Gérard Céline
  • N'Guyen Franck
  • Osipov Nikolay
  • Cailletaud Georges
  • Bornert Michel
  • Caldemaison Daniel
  Computational Materials Science, Elsevier, 2009, 46, pp.755-760. The plastic behaviour of FCC materials is studied under cyclic tensile–compression loading at room temperature. The material is an oxygen-free high conductivity copper. The purpose of the work is to model the onset of plasticity, then the cycle by cycle evolution of the localized strain, at grain scale and at mesoscopic scale. A polycrystalline aggregate taking into account the material microstructure is developped to perform finite element simulations corresponding to the experiments. Finite element calculations are carried out on this mesh, using a constitutive law which takes into account the crystallographic orientation of each grain. An analysis of the localisation scheme is performed at different steps of the cyclic loading. (10.1016/j.commatsci.2009.04.037)
  DOI : 10.1016/j.commatsci.2009.04.037
• Micromechanical approach to the strength properties of frictional geomaterials
  
  • Maghous Samir
  • Dormieux Luc
  • Barthélémy Jean-François
  European Journal of Mechanics - A/Solids, Elsevier, 2009, 28 (1), pp.179-188. The present paper describes a micromechanics-based approach to the strength properties of composite materials with a Drucker–Prager matrix in the situation of non-associated plasticity. The concept of limit stress states for such materials is first extended to the context of homogenization. It is shown that the macroscopic limit stress states can theoretically be obtained from the solution to a sequence of viscoplastic problems stated on the representative elementary volume. The strategy of resolution implements a non-linear homogenization technique based on the modified secant method. This procedure is applied to the determination of the macroscopic strength properties and plastic flow rule of materials reinforced by rigid inclusions, as well as for porous media. The role of the matrix dilatancy coefficient is in particular discussed in both cases. Finally, finite element solutions are derived for a porous medium and compared to the micromechanical predictions. (10.1016/j.euromechsol.2008.03.002)
  DOI : 10.1016/j.euromechsol.2008.03.002
• Influence of boundary conditions on strain field analysis for polycrystalline finite element simulations
  
  • Héripré Eva
  • Crépin Jérôme
  • Roos Arjen
  • Chaboche Jean Louis
  Revue Européenne de Mécanique Numérique/European Journal of Computational Mechanics, Hermès / Paris : Lavoisier, 2009, 18, pp.333-351. his paper presents a first validation of a novel methodology for identifying the parameters of a crystallographic elastoplastic constitutive law. This is accomplished by comparing simulation and experimental results at different length scales: the microstructure scale and the representative volume element scale. Experimentally, the microscopic strain fields and the microstrucural characteristics can be obtained only at the surface of the specimen. As a consequence, in finite element simulations only at the surface there is a oneto-one correspondence between the mesh and the experimental observed grain morphology. In this paper, the morphology of the subsurface grains is obtained by a simple extension in the thickness direction of the surface morphology. The aim of this study is then to verify whether the surface data contain sufficient information for the identification of the parameters of the constitutive law. (10.3166/ejcm.18.333-351)
  DOI : 10.3166/ejcm.18.333-351
• Modélisation et Calcul des Milieux Continus
  
  • Le Tallec Patrick
  , 2009, pp.550.
• Multiscale approach of mechanical behaviour of SiC/SiC composites : elastic behaviour at the scale of the tow
  
  • Chateau Camille
  • Gélébart Lionel
  • Bornert Michel
  • Crépin Jérôme
  • Caldemaison Daniel
  , 2010, 30 (1-3), pp.45-55. SiC/SiC composites are candidates for structural applications at elevated temperatures in the context of the development of the 4th generation of nuclear reactors. A multiscale approach is under development to construct a predictive modelling of their complex mechanical behaviour due to their heterogeneous microstructure. This approach is based on two scale transitions: from the fibres/matrix microstructure to the tow and from the tow to the woven composite, each scale presenting a significant residual porosity. This paper focuses on the first scale transition and on the modelling of the elastic behaviour of the tow at room temperature. A microstructural investigation of several tows in a 2D SiC/SiC specimen has been conducted using scanning electron microscopy to get statistical data on microstructural characteristics by image analysis in order to generate a virtual microstructure. The elastic problem of homogenisation is numerically solved by means of finite element techniques. The simulations performed on various volumes show noticeable fluctuations of the apparent behaviour: so separation of length scales is not satisfied in this material. Nevertheless, this problem is neglected in a first approximation and the homogeneous equivalent behaviour is evaluated by averaging the apparent behaviours of several volume elements - smaller than the Representative Volume Element (RVE) – called Statistical Volume Elements (SVEs). Finally, influence of porosity and pores' morphology is quantified.
• Assessment of digital image correlation measurement errors: methodology and results
  
  • Bornert Michel
  • Brémand Fabrice
  • Doumalin Pascal
  • Dupré Jean-Christophe
  • Fazzini Marina
  • Grédiac Michel
  • Hild François
  • Mistou Sebastien
  • Molimard Jérôme
  • Orteu Jean-José
  • Robert Laurent
  • Surrel Yves
  • Vacher Pierre
  • Wattrisse Bertrand
  Experimental Mechanics, Society for Experimental Mechanics, 2009, 49, pp.353-370. Optical full-field measurement methods such as Digital Image Correlation (DIC) are increasingly used in the field of experimental mechanics, but they still suffer from a lack of information about their metrological performances. To assess the performance of DIC techniques and give some practical rules for users, a collaborative work has been carried out by the Workgroup "Metrology" of the French CNRS research network 2519 "MCIMS (Mesures de Champs et Identification en Mécanique des Solides / Full-field measurement and identification in solid mechanics, http://www.ifma.fr/lami/gdr2519)". A methodology is proposed to assess the metrological performances of the image processing algorithms that constitute their main component, the knowledge of which being required for a global assessment of the whole measurement system. The study is based on displacement error assessment from synthetic speckle images. Series of synthetic reference and deformed images with random patterns have been generated, assuming a sinusoidal displacement field with various frequencies and amplitudes. Displacements are evaluated by several DIC packages based on various formulations and used in the French community. Evaluated displacements are compared with the exact imposed values and errors are statistically analyzed. Results show general trends rather independent of the implementations but strongly correlated with the assumptions of the underlying algorithms. Various error regimes are identified, for which the dependence of the uncertainty with the parameters of the algorithms, such as subset size, gray level interpolation or shape functions, is discussed. (10.1007/s11340-008-9204-7)
  DOI : 10.1007/s11340-008-9204-7
• Crack identification by 3D time-domain elastic or acoustic topological sensitivity
  
  • Bellis Cédric
  • Bonnet Marc
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2009, 337, pp.124-130. The topological sensitivity analysis, based on the asymptotic behaviour of a cost functional associated with the creation of a small trial flaw in a defect-free solid, provides a computationally-fast, non-iterative approach for identifying flaws embedded in solids. This concept is here considered for crack identification using time-dependent measurements on the external boundary. The topological derivative of a cost function under the nucleation of a crack of infinitesimal size is established, in the framework of time-domain elasticity or acoustics. The simplicity and efficiency of the proposed formulation is enhanced by the recourse to an adjoint solution. Numerical results obtained on a 3-D elastodynamic example using the conventional FEM demonstrate the usefulness of the topological derivative as a crack indicator function. (10.1016/j.crme.2009.03.015)
  DOI : 10.1016/j.crme.2009.03.015
• Plasticity and Fracture of Martensitic Boron Steel Under Plane Stress Conditions
  
  • Ebnöther Fabien
  • Mohr Dirk
  International Journal of Solids and Structures, Elsevier, 2009, pp.3535-3547.
• A new fast multi-domain BEM to model seismic wave propagation and amplification in 3D geological structures
  
  • Chaillat Stéphanie
  • Bonnet Marc
  • Semblat Jean-François
  Geophysical Journal International, Oxford University Press (OUP), 2009, 177, pp.509-531. The analysis of seismic wave propagation and amplification in complex geological structures raises the need for efficient and accurate numerical methods. The solution of the elastodynamic equations using traditional boundary element methods (BEMs) is greatly hindered by the fully-populated nature of the matrix equations arising from the discretization. In a previous study limited to homogeneous media, the present authors have established that the Fast Multipole (FM) method reduces the complexity of a 3-D elastodynamic BEM to $N \log N$ per GMRES iteration and demonstrated its effectiveness on 3-D canyon configurations. In this article, the frequency-domain FM-BEM methodology is extented to 3-D elastic wave propagation in piecewise-homogeneous domains in the form of a FM-accelerated multi-region BE-BE coupling approach. This new method considerably enhances the capability of the BEM for studying the propagation of seismic waves in 3-D alluvial basins of arbitrary geometry embedded in semi-infinite media. Several fully 3-D examples (oblique SV-waves) representative of such configurations validate and demonstrate the capabilities of the multi-domain fast multipole approach. They include comparisons with available (low-frequency) results for various types of incident wavefields, and time-domain results obtained by means of Fourier synthesis. (10.1111/j.1365-246X.2008.04041.x)
  DOI : 10.1111/j.1365-246X.2008.04041.x
• Influence of free water on the quasi-static and dynamic strength of concrete in confined compression tests
  
  • Forquin Pascal
  • Safa Kamal
  • Gary Gérard
  Cement and Concrete Research, Elsevier, 2009, 40 (2), pp.321-333. The behaviour of concrete under high pressure and dynamic loadings is experimentally investigated in the present paper. The specimen is confined in a cylindrical elastic steel ring that insures a quasi-uniaxial strain state of loading. It is subjected to static and dynamic (with strain rates in the range from 1e−6/s to 200/s) axial compressive loadings. Transverse gauges glued on the lateral surface of the ring allow for the measurement of the confining pressure so that the volumetric and the deviatoric response of the specimen can be computed. At high or intermediate strain rates, water saturated and dried specimens show strongly different results: i.e. a continuous increase of strength with pressure in dried specimens and a quasi nil strength enhancement in water-saturated specimens. This difference is not observed with quasi-static loadings. As explained through a basic poromechanics analysis, this dissimilarity is mainly attributed to an increase of pore pressure inside the saturated concrete during fast (quasi-static or dynamic) experiments. (10.1016/j.cemconres.2009.09.024)
  DOI : 10.1016/j.cemconres.2009.09.024
• Dynamic Behavior of Concrete: Experimental aspects
  
  • Toutlemonde François
  • Gary Gérard
  , 2009, pp.1-47. (10.1002/9780470611555.ch1)
  DOI : 10.1002/9780470611555.ch1
• Hardening description for FCC materials under complex loading paths
  
  • Gérard Céline
  • Bacroix Brigitte
  • Bornert Michel
  • Cailletaud Georges
  • Crépin Jérôme
  • Leclercq Sylvain
  Computational Materials Science, Elsevier, 2009, 45, pp.751-755. The present work aims at exploring self and latent hardening for FCC polycrystals under complex loading paths at room temperature. Combinations of simple loading paths sequences, such as tension and simple shear, with different orientations with regard to rolling direction, are considered. Experimental results are compared to finite element computations of polycrystalline aggregates taking into account the material microstructure, and to simulations based on mean field models. (10.1016/j.commatsci.2008.08.027)
  DOI : 10.1016/j.commatsci.2008.08.027
• Méthodes numériques rapides non-itératives en diffraction inverse élastodynamique basées sur l'asymptotique topologique de fonctions coût
  
  • Bellis Cédric
  • Bonnet Marc
  • Guzina B. B.
  , 2009.
• Multiscale thermomechanical modeling of shock-driven dry friction in hydrodynamics
  
  • Dambakazi Franck
  • Le Tallec Patrick
  • Perlat Jean-Philippe
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2009, 198 (21-26), pp.1701-1715. The purpose of the present work is to provide new insights in the understanding and computational modeling of shock-induced metal-on-metal dry friction. Based on a multiscale approach, we develop herein a 1D finite difference subgrid model. To adequately describe the physics of dynamic friction under shock-induced conditions, it accounts for frictional contact, elastoplastic yielding and work hardening, heating by friction and plastic work, thermal softening and melting, as well as dynamics effects. Temperature and dynamic elastoplasticity are predicted at a local scale through a nonlinear time implicit numerical solver. Two strategies have been considered for the coupling of the subgrid model to a standard thermoelastoplastic macroscopic model. The first one is velocity driven. Its implementation is rather straightforward, it leads to correct qualitative results but is restricted to sliding situations. To account for stick–slip cases, a second force driven downscaling strategy has been developed. (10.1016/j.cma.2008.12.019)
  DOI : 10.1016/j.cma.2008.12.019
• Viscoélasticité pour le calcul des structures
  
  • Salençon Jean
  , 2009, pp.151.
• Experimental device for chemical osmosis measurement on natural clay-rock samples maintained at in situ conditions: Implications for formation pressure interpretations
  
  • Rousseau-Gueutin Pauline
  • de Greef Vincent
  • Gonçalvès Julio
  • Violette Sophie
  • Chanchole Serge
  Journal of Colloid and Interface Science, Elsevier, 2009, 337 (1), pp.106 - 116. In order to characterize the so-called coupled processes occurring in compacted clay rocks, the coupling coefficients must be identified. For this purpose, an original device which allows such measurement for undisturbed (natural) samples in their in situ conditions was developed. The present experimental device minimizes the fluid leaks improving the accuracy of the coupling parameter determination. Three chemical osmotic tests were performed on a cylindrical sample of Callovo-Oxfordian argilite. Room temperature variations during the chemical osmosis experiments required the implementation of temperature effects in the numerical model used for the interpretations. These variations offered the opportunity of an alternative method to estimate the compressibility of the fluid in the circuit connected to a measurement chamber located in the center of the sample. An osmotic efficiency of almost 0.2 for a concentration of 0.094 mol L-1 is obtained for the Callovo-Oxfordian argilite. This value would explain only some part (approximately 0.10-0.15 MPa) of the overpressures (0.5-0.6 MPa) relative to the surrounding reservoirs measured in this formation. Others processes, such as thermo-osmosis, hydrodynamic boundary condition changes due to climate variations or creep behavior of the shale, could explain the remainder of the overpressures. (10.1016/j.jcis.2009.04.092)
  DOI : 10.1016/j.jcis.2009.04.092
• On a nonlinear inverse problem in viscoelasticity
  
  • Bui Huy Duong
  • Chaillat Stéphanie
  Vietnam Journal of Mechanics, Viện Hàn Lâm Khoa học và Công nghệ Việt Nam, 2009, 31, pp.211-219. We consider an inverse problem for determining an inhomogeneity in a viscoelastic body of the Zener type, using Cauchy boundary data, under cyclic loads at low frequency. We show that the inverse problem reduces to the one for the Helmholtz equation and to the same nonlinear Calderon equation given for the harmonic case. A method of solution is proposed which consists in two steps : solution of a source inverse problem, then solution of a linear Volterra integral equation.
• Cyclic approximation of the heat equation in finite strains for the build-up problem of rubber
  
  • Le Chenadec Yohann
  • Raoult Ida
  • Stolz Claude
  • Nguyen Thi Mac Lan
  Journal of Mechanics of Materials and Structures, Mathematical Sciences Publishers, 2009, 4 (2), pp.309-318.
• The effective behavior of (heterogeneous) elastic bodies containing defects localized on a surface
  
  • Marigo Jean-Jacques
  • Pideri Catherine
  , 2009.
• A finite-strain model for anisotropic viscoplastic porous media: II – Applications
  
  • Danas Kostas
  • Ponte Castañeda Pedro
  European Journal of Mechanics - A/Solids, Elsevier, 2009, 28, pp.402-416. In Part I of this work, we have proposed a new model based on the "second-order" nonlinear homogenization method for determining the effective response and microstructure evolution in viscoplastic porous media with aligned ellipsoidal voids subjected to general loading conditions. In this second part, the new model is used to analyze the instantaneous effective behavior and microstructure evolution in porous media for several representative loading conditions and microstructural configurations. First, we study the effect of the shape and orientation of the voids on the overall instantaneous response of a porous medium that is subjected to principal loading conditions. Secondly, we study the problem of microstructure evolution under axisymmetric and simple shear loading conditions for initially spherical voids in an attempt to validate the present model by comparison with existing numerical and approximate results in the literature. Finally, we study the possible development of macroscopic instabilities for the special case of ideally-plastic solids subjected to plane-strain loading conditions. The results, reported in this paper, suggest that the present model improves dramatically on the earlier "variational" estimates, in particular, because it generates much more accurate results for high triaxiality loading conditions. (10.1016/j.euromechsol.2008.11.003)
  DOI : 10.1016/j.euromechsol.2008.11.003
• Elastic-wave identification of penetrable obstacles using shape-material sensitivity framework
  
  • Bonnet Marc
  • Guzina B. B.
  Journal of Computational Physics, Elsevier, 2009, 228, pp.294-311. This study deals with elastic-wave identification of discrete heterogeneities (inclusions) in an otherwise homogeneous ``reference'' solid from limited-aperture waveform measurements taken on its surface. On adopting the boundary integral equation (BIE) framework for elastodynamic scattering, the inverse query is cast as a minimization problem involving experimental observations and their simulations for a trial inclusion that is defined through its boundary, elastic moduli, and mass density. For an optimal performance of the gradient-based search methods suited to solve the problem, explicit expressions for the shape (i.e. boundary) and material sensitivities of the misfit functional are obtained via the adjoint field approach and direct differentiation of the governing BIEs. Making use of the message-passing interface, the proposed sensitivity formulas are implemented in a data-parallel code and integrated into a nonlinear optimization framework based on the direct BIE method and an augmented Lagrangian whose inequality constraints are employed to avoid solving forward scattering problems for physically inadmissible (or overly distorted) trial inclusion configurations. Numerical results for the reconstruction of an ellipsoidal defect in a semi-infinite solid show the effectiveness of the proposed shape-material sensitivity formulation, which constitutes an essential computational component of the defect identification algorithm. (10.1016/j.jcp.2008.09.009)
  DOI : 10.1016/j.jcp.2008.09.009
• Le sous-sol peut-il être étanche ?
  
  • Berest Pierre
  • Bérest P.
  , 2009.