Publications

2008

• 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.
• 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
• 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
• 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
• 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
• Quoi de neuf ? La mécanique !
  
  • Salençon Jean
  Mechanics & Industry, EDP Sciences, 2008, 9 (4), pp.255-259. (10.1051/meca:2008031)
  DOI : 10.1051/meca:2008031
• Mechanical Behaviour of a Marly Floor in two Mines where Brine or Water was abundant
  
  • Berest Pierre
  • Bérest P.
  , 2008, pp.19-40.
• The 1873 Collapse of the Saint-Maximilien Panel at the Varangéville Salt Mine.
  
  • Berest Pierre
  • Bérest P.
  • Karimi-Jafari Mehdi
  • Feuga Bernard
  • Brouard Benoît
  Int. J. Rock Mech. Min. Sc., 2008 (n°45), pp.1025-1043.
• Renormalizations in solid and fracture mechanics
  
  • Bui Huy Duong
  Journal of Mechanics of Materials and Structures, Mathematical Sciences Publishers, 2008, 3 (5), pp.853-866. We show how some inconstencies and infinities arising in solid and fracture mechanics can be avoided by renormalization techniques widely used in theoretical physics. Some examples, already known in solid mechanics or recently discovered in fracture mechanics, are given as illustration.
• Haptic Interface for Musical Keyboards
  
  • Lozada José
  • Hafez Moustapha
  • Boutillon Xavier
  , 2008, pp.4 p.. We present a novel haptic interface for musical keyboards aimed to reproduce the dynamic behavior of grand-piano action mechanism based on magneto-rheological fluids. The intrinsic dissipative characteristic of MR fluids ensures passivity making them appealing for the use in haptic interface. The interface is composed of three main parts: an active damping system, a mechanical structure, sensors and electronics needed for control. The damping system uses a thin magnetic plate to shear the MR fluid contained into the gap. When a magnetic field is applied, the fluid apparent viscosity increases generating a resistive force against the motion of the plate set by the user. An experimental device used for the MR fluid behavior identification is also presented.
• An implicit energetic approach of 3d crack growth under fatigue loading and residual stresses
  
  • Chiaruttini Vincent
  • Edeline Gwenael
  • Feyel Frédéric
  • Bonnet Marc
  , 2008.