Publications

2008

• A New Experimental Technique for the Multi-axial Testing of Advanced High Strength Steel
  
  • Mohr Dirk
  • Oswald M.
  Experimental Mechanics, Society for Experimental Mechanics, 2008, pp.65-77.
• Large Deformation of Anisotropic Austenitic Stainless Steel Sheets at Room Temperature: Multi-axial Experiments and Phenomenological Modeling
  
  • Mohr Dirk
  • Jacquemin Johan
  Journal of the Mechanics and Physics of Solids, Elsevier, 2008, pp.2935-2956.
• Combined shape-material sensitivity for elastic-wave identification of penetrable inclusions
  
  • Bonnet Marc
  • Guzina B. B.
  , 2008.
• Instruments à cordes frottées
  
  • Boutillon Xavier
  , 2008, pp.511-532 et 132-135.
• Travelling interface waves in a brake-like system under unilateral contact and Coulomb friction
  
  • Nguyen Quoc Son
  • Oueslati Abdelbacet
  • Steindl Alois
  • Teufel Andreas
  • Troger Hans
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2008, 336 (1-2), pp.203-209. This article considers the frictional interface waves generated by the flutter instability of the sliding steady state for an elastic tube in frictional contact with a rigid and rotating shaft. According to the values of the contact pressure, the rotation velocity and the friction coefficient, several periodic dynamical responses can be found under the form of travelling surface waves. Examples of stick-slip, stick-slip-separation and stick-slip-separation-reverse-slip waves are reported here. Some discussions on the stability of these waves are also given. (10.1016/j.crme.2007.11.011)
  DOI : 10.1016/j.crme.2007.11.011
• A homogenization-based constitutive model for two-dimensional viscoplastic porous media
  
  • Danas Kostas
  • Idiart Martin I.
  • Ponte Castañeda Pedro
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2008, 336, pp.79-90. An approximate model based on the so-called "second-order" nonlinear homogenization method is proposed to estimate the effective behavior of viscoplastic porous materials exhibiting transversely isotropic symmetry. The model is constructed in such a way that it reproduces exactly the behavior of a "composite-cylinder assemblage" in the limit of in-plane hydrostatic loading, and therefore coincides with the hydrostatic limit of Gurson's criterion for plastic porous materials. As a consequence, the new model improves on earlier "second-order" homogenization estimates, which have been found to be overly stiff at sufficiently high triaxialities and nonlinearities. 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 excellent for the entire range of stress triaxialities, and all values of the porosity and nonlinearity considered. (10.1016/j.crme.2007.10.017)
  DOI : 10.1016/j.crme.2007.10.017
• Joint state and parameter estimation for distributed mechanical systems
  
  • Moireau Philippe
  • Chapelle Dominique
  • Le Tallec Patrick
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2008, 197 (6-8), pp.659-677. We present a novel strategy to perform estimation for a dynamical mechanical system in standard operating conditions, namely, without ad hoc experimental testing. We adopt a sequential approach, and the joint state-parameter estimation procedure is based on a state estimator inspired from collocated feedback control. This type of state estimator is chosen due to its particular effectiveness and robustness, but the methodology proposed to adequately extend state estimation to joint state-parameter estimation is general, and - indeed -applicable with any other choice of state feedback observer. The convergence of the resulting joint estimator is mathematically established. In addition, we demonstrate its effectiveness with a biomechanical test problem defined to feature the same essential characteristics as a heart model, in which we identify localized contractility and stiffness parameters using measurements of a type that is available in medical imaging. (10.1016/j.cma.2007.08.021)
  DOI : 10.1016/j.cma.2007.08.021
• A multi-level fast multipole BEM for 3-D elastodynamics in the frequency domain
  
  • Chaillat Stéphanie
  • Bonnet Marc
  • Semblat Jean-François
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2008, 197, pp.4233--4249. To reduce computational complexity and memory requirement for 3-D elastodynamics using the boundary element method (BEM), a multi-level fast multipole BEM (FM-BEM) is proposed. The diagonal form for the expansion of the elastodynamic fundamental solution is used, with a truncation parameter adjusted to the subdivision level, a feature necessary for achieving optimal computational efficiency. Both the single-level and multi-level forms of the elastodynamic FM-BEM are considered, with emphasis on the latter. Crucial implementation issues, including the truncation of the multipole expansion, the optimal number of levels, the direct and inverse extrapolation steps are examined in detail with the backing of numerical experiments. A complexity analysis for both the single-level and multi-level versions is conducted. The correctness and computational performances of the proposed elastodynamic FMM are demonstrated on numerical examples, featuring up to $O(10^{6})$ DOFs run on a single-processor PC and including the diffraction of an incident P plane wave by a semi-spherical or semi-ellipsoidal canyon, representative of topographic site effects. (10.1016/j.cma.2008.04.024)
  DOI : 10.1016/j.cma.2008.04.024
• Adiabatic temperature changes in an oil-filled cavern.
  
  • Berest Pierre
  • Bérest P.
  , 2008, pp.81-103.
• Fast non-iterative methods for defect identification
  
  • Bonnet Marc
  • Guzina B. B.
  • Nemitz N.
  Revue Européenne de Mécanique Numérique/European Journal of Computational Mechanics, Hermès / Paris : Lavoisier, 2008, 17, pp.571-582. This communication summarizes recent investigations on the identification of defects (cavities, inclusions) of unknown geometry and topology by means of the concept of topological sensitivity. This approach leads to the fast computation (equivalent to performing a few direct solutions), by means of ordinary numerical solution methods such as the BEM (used here), the FEM or the FDM, of defect indicator functions. Substantial further acceleration is obtained by using fast multipole accelerated BEMs. Possibilities afforded by this approach are demonstrated on numerical examples. The paper concludes with a discussion of further research on theoretical and numerical issues. (10.3166/remn.17.571-582)
  DOI : 10.3166/remn.17.571-582
• Multiscale modeling of oriented thermoplastic elastomers with lamellar morphology
  
  • Lopez-Pamies O.
  • Garcia R.
  • Chabert E.
  • Cavaillé J.-Y.
  • Ponte Castañeda P.
  Journal of the Mechanics and Physics of Solids, Elsevier, 2008, 56 (11), pp.3206-3223. Thermoplastic elastomers (TPEs) are block copolymers made up of "hard" (glassy or crystalline) and "soft" (rubbery) blocks that self-organize into "domain" structures at a length scale of a few tens of nanometers. Under typical processing conditions, TPEs also develop a "polydomain" structure at the micron level that is similar to that of metal polycrystals. Therefore, from a continuum point of view, TPEs may be regarded as materials with heterogeneities at two different length scales. In this work, we propose a constitutive model for highly oriented, near-single-crystal TPEs with lamellar domain morphology. Based on small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) observations, we consider such materials to have a granular microstructure where the grains are made up of the same, perfect, lamellar structure (single crystal) with slightly different lamination directions (crystal orientations). Having identified the underlying morphology, the overall finite-deformation response of these materials is determined by means of a two-scale homogenization procedure. Interestingly, the model predictions indicate that the evolution of microstructure-especially the rotation of the layers-has a very significant, but subtle effect on the overall properties of near-single-crystal TPEs. In particular, for certain loading conditions-namely, for those with sufficiently large compressive deformations applied in the direction of the lamellae within the individual grains-the model becomes macroscopically unstable (i.e., it loses strong ellipticity). By keeping track of the evolution of the underlying microstructure, we find that such instabilities can be related to the development of "chevron" patterns. © 2008 Elsevier Ltd. All rights reserved. (10.1016/j.jmps.2008.07.008)
  DOI : 10.1016/j.jmps.2008.07.008
• Discussion of "Second order topological sensitivity analysis" by J. Rocha de Faria et al
  
  • Bonnet Marc
  International Journal of Solids and Structures, Elsevier, 2008, 45, pp.705-707. The article by J. Rocha de Faria et al. under discussion is concerned with the evaluation of the perturbation undergone by the potential energy of a domain $\Omega$ (in a 2-D, scalar Laplace equation setting) when a disk $B_{\epsilon}$ of small radius $\epsilon$ centered at a given location $\hat{\boldsymbol{x}\in\Omega$ is removed from $\Omega$, assuming either Neumann or Dirichlet conditions on the boundary of the small `hole' thus created. In each case, the potential energy $\psi(\Omega_{\epsilon})$ of the punctured domain $\Omega_{\epsilon}=\Omega\setminus\B_{\epsilon}$ is expanded about $\epsilon=0$ so that the first two terms of the perturbation are given. The first (leading) term is the well-documented topological derivative of $\psi$. The article under discussion places, logically, its main focus on the next term of the expansion. However, it contains incorrrect results, as shown in this discussion. In what follows, equations referenced with Arabic numbers refer to those of the article under discussion.
• A testing technique for concrete under confinement at high rates of strain
  
  • Forquin Pascal
  • Gary Gerard
  • Gatuingt Fabrice
  International Journal of Impact Engineering, Elsevier, 2008, 35 (6), pp.425-446. A testing device is presented for the experimental study of dynamic compaction of concrete under high strain rates. The specimen is confined in a metallic ring and loaded by means of a hard-steel Hopkinson pressure bar (80 mm diameter, 6 m long) allowing for the testing of specimens large enough regarding the aggregate size. The constitutive law for the metal of the ring being known, transverse gauges glued on its lateral surface allow for the measurement of the confining pressure. The hydrostatic and deviatoric responses of the specimen can then be computed. The proposed method is validated by several numerical simulations of tests involving a set of four different concrete-like behaviours and different friction coefficients between the cell and the specimen. Finally, three tests performed with the MB50 concrete at three different strain rates are processed with the method and are compared with literature results for the same material under quasi-static loadings. (10.1016/j.ijimpeng.2007.04.007)
  DOI : 10.1016/j.ijimpeng.2007.04.007
• Reproducibility of piano playing
  
  • Principeaud Nicolas
  • Boutillon Xavier
  , 2008, 123 (5 Pt 2), pp.3125. (10.1121/1.2933054)
  DOI : 10.1121/1.2933054
• A complex model for piano action
  
  • Lozada José
  • Boutillon Xavier
  • Hafez Moustapha
  , 2008, 123 (5 Pt. 2), pp.3660. (10.1121/1.2934975)
  DOI : 10.1121/1.2934975