Publications

2014

• Influence of fillers and bonding agents on the viscoelasticity of highly filled elastomers
  
  • Azoug Aurélie
  • Nevière Robert
  • Pradeilles-Duval Rachel-Marie
  • Constantinescu Andrei
  Journal of Applied Polymer Science, Wiley, 2014, 131 (16). Highly filled elastomers such as solid propellants exhibit a complex nonlinear viscoelastic behavior. This work aimed at determining the influence of binder-filler and filler-filler interactions on the microstructure and the viscoelastic properties of the propellant using a design of experiments method. The influences of the filler fraction and of the filler–binder bonding agents (FBBA) were measured by swelling experiments and prestrained dynamic mechanical analyses. The results showed that FBBA react on the filler surface and concentrate the curing agents in the vicinity of the fillers. The nonlinearity of the viscoelastic behavior originated from filler-filler interactions that created high stress zones between fillers and therefore constrained the movements of the macromolecules of the binder. Filler-binder interactions induced by the FBBA increased the filler effective volume as well as the heterogeneous stress distribution in the microstructure. (10.1002/app.40664)
  DOI : 10.1002/app.40664
• Asymptotic analysis of small defects near a singular point in antiplane elasticity, with an application to the nucleation of a crack at a notch
  
  • Bach Thi
  • Dang Tuyet
  • Halpern Laurence
  • Marigo Jean-Jacques
  Mathematics and Mechanics of Complex Systems, International Research Center for Mathematics & Mechanics of Complex Systems (M&MoCS),University of L’Aquila in Italy, 2014, 2 (2), pp.141-179. We use matching asymptotic expansions to treat the antiplane elastic problem associated with a small defect located at the tip of a notch. In a first part, we develop the asymptotic method for any type of defect and present the sequential procedure which allows us to calculate the different terms of the inner and outer expansions at any order. This requires in particular separating in each term its singular part from its regular part. In a second part, the asymptotic method is applied to the case of a crack of variable length located at the tip of a given notch. We show that the first two nontrivial terms of the expansion of the energy release rate are sufficient to well approximate the dependence of the energy release rate on the crack length in the range of values of the length which are sufficient to treat the problem of nucleation. This problem is considered in the last part where we compare the nucleation and the propagation of a crack predicted by two different models: the classical Griffith law and the Francfort–Marigo law based on an energy minimization principle. Several numerical results illustrate the interest of the method. (10.2140/memocs.2014.2.141)
  DOI : 10.2140/memocs.2014.2.141
• Dynamic Stability of Externally Pressurized Elastic Rings Subjected to High Rates of Loading
  
  • Putelat T.
  • Triantafyllidis Nicolas
  International Journal of Solids and Structures, Elsevier, 2014, 51, pp.1 - 12. Of interest here is the influence of loading rate on the stability of structures where inertia is taken into account, with particular attention to the comparison between static and dynamic buckling. This work shows the importance of studying stability via perturbations of the initial conditions, since a finite velocity governs the propagation of disturbances. The method of modal analysis that determines the fastest growing wavelength, currently used in the literature to analyze dynamic stability problems, is meaningful only for cases where the velocity of the perfect structure is significantly lower than the associated wave propagation speeds. As a model structure to illustrate this point we select an elastic ring subjected to external hydrostatic pressure which is applied at different rates epsilon (appropriately non-dimensionalized with respect to elastic axial wave speed). The ring's stability is studied by following the evolution of a localized small perturbation. It is shown that for small values of the applied loading rate, the structure fails through a global mode, while for large values of the applied loading rate the structure fails by a localized mode of deformation. An analytically obtained localization time t(1) is found to be a very good estimate of the onset of instability time at high loading rates (10.1016/j.ijsolstr.2013.08.002)
  DOI : 10.1016/j.ijsolstr.2013.08.002
• Instability of a magnetoelastic layer resting on a non-magnetic substrate
  
  • Danas Kostas
  • Triantafyllidis Nicolas
  Journal of the Mechanics and Physics of Solids, Elsevier, 2014, 69, pp.67-83. Magnetorheological elastomers (MREs) are ferromagnetic particle impregnated rubbers whose mechanical properties are altered by the application of external magnetic fields. Due to their coupled magneto-mechanical response, MREs are finding an increasing number of engineering applications. One such application is in haptics, where the goal is to actively control surface roughness. One way to achieve this is by exploiting the unstable regime of MRE substrate/layer assemblies subjected to transverse magnetic fields. In this work, we study the response of such an assembly subjected to a transverse magnetic field and in-plane stress. The layer is made up of a transversely isotropic MRE material, whose energy density has been obtained experimentally, while the substrate is a non-magnetic isotropic pure polymer/gel. An analytical solution to this problem based on a general, finite strain, 2D continuum modeling for both the MRE layer and the substrate, shows that for adequately soft substrates there is a finite-wavelength buckling mode under a transverse magnetic field. Moreover, the critical magnetic field can be substantially reduced in the presence of a compressive stress of the assembly, thus opening the possibility for haptic applications operating under low magnetic fields.
• Mathematical modelling of multi conductor cables
  
  • Beck Geoffrey
  • Imperiale Sebastien
  • Joly Patrick
  Discrete and Continuous Dynamical Systems - Series S, American Institute of Mathematical Sciences, 2014, pp.26. This paper proposes a formal justification of simplified 1D models for the propagation of electromagnetic waves in thin non-homogeneous lossy conductor cables. Our approach consists in deriving these models from an asymptotic analysis of 3D Maxwell’s equations. In essence, we extend and complete previous results to the multi-wires case. (10.3934/dcdss.2015.8.521)
  DOI : 10.3934/dcdss.2015.8.521
• Editorial
  
  • Bérest Pierre
  Oil & Gas Science and Technology - Revue d'IFP Energies nouvelles, Institut Français du Pétrole (IFP), 2014, 69 (7), pp.1135-1141. No abstract available (10.2516/ogst/2014049)
  DOI : 10.2516/ogst/2014049
• Statistical inverse method for the multiscale identification of the apparent random elasticity field of heterogeneous microstructures
  
  • Soize Christian
  • Desceliers Christophe
  • Guilleminot Johann
  • Nguyen M. T.
  • Allain Jean-Marc
  • Gharbi H.
  , 2014.
• Modelling the dynamics of the piano action: is apparent success real?
  
  • Thorin Anders
  • Boutillon Xavier
  • Lozada José
  Acta Acustica united with Acustica, Hirzel Verlag, 2014, pp.10. The kinematics and the dynamics of the piano action mechanism have been much studied in the last 50 years and fairly sophisticated models have been proposed in the last decade. Surprisingly, simple as well as sophisticated models seem to yield very valuable simulations when compared to measurements. We propose here a very simple model, with only 1-degree of freedom, and compare its outcome with force and motion measurements obtained by playing a real piano mechanism. The model, purposely chosen as obviously too simple to be predictive of the dynamics of the grand piano action, appears either as very good or as very bad, depending on which physical quantities are used as the input and output. We discuss the sensitivity of the simulation results to the initial conditions and to noise and the sensitivity of the experimental/simulation comparisons to the chosen dynamical model. It is shown that force-driven simulations with position comparisons, as they are proposed in the literature, do not validate the dynamical models of the piano action. It is suggested that these models be validated with position-driven simulations and force comparisons. (10.3813/AAA.918795)
  DOI : 10.3813/AAA.918795
• Multi-scale mechanical characterization of sound dentin
  
  • Wang Wenlong
  • Vennat Elsa
  • Puel Guillaume
  • Roubier Nicolas
  • Allain Jean-Marc
  • Attal Jean-Pierre
  , 2014.