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Chasseneuil-du-Poitou, France

De Saxce G.,Lille Laboratory of Mechanics | Vallee C.,Laboratoire Of Mecanique Des Solides
Mathematics and Mechanics of Solids | Year: 2012

In a previous paper, we proposed an approach for the dynamics of 3D bodies and shells based on the use of affine tensors. This new theoretical frame is very large and the applications are not limited to the mechanics of continua. In the present paper, we show how it can be also applied to the description of the mechanics of freely falling particles and rigid bodies. The mass, the linear and angular momenta are structured as a single object called a torsor. Excluding all metric notions, we define the torsors as skew-symmetric bilinear mappings operating on the linear space of the affine functions. Torsors are a particular family of affine tensors. On this ground, we define an intrinsic differential operator called the affine covariant derivative. Next, we claim that the torsor characterizing the behaviour of a freely falling particle is affine covariant derivative free, that allows recovering both laws of linear and angular momentum. Finally, it is shown how the motion of rigid bodies can be described within this frame. © The Author(s) 2011.

Danas K.,University of Cambridge | Danas K.,Laboratoire Of Mecanique Des Solides | Deshpande V.S.,University of Cambridge | Fleck N.A.,University of Cambridge
International Journal of Plasticity | Year: 2010

Discrete dislocation plasticity models and strain-gradient plasticity theories are used to investigate the role of interfaces in the elastic-plastic response of a sheared single crystal. The upper and lower faces of a single crystal are bonded to rigid adherends via interfaces of finite thickness. The sandwich system is subjected to simple shear, and the effect of thickness of crystal layer and of interfaces upon the overall response are explored. When the interface has a modulus less than that of the bulk material, both the predicted plastic size effect and the Bauschinger effect are considerably reduced. This is due to the relaxation of the dislocation stress field by the relatively compliant surface layer. On the other hand, when the interface has a modulus equal to that of the bulk material a strong size effect in hardening as well as a significant reverse plasticity are observed in small specimens. These effects are attributed to the energy stored in the elastic fields of the geometrically necessary dislocations (GNDs). © 2010 Elsevier Ltd. All rights reserved.

Bouchoucha F.,University of Sfax | Bouchoucha F.,Ecole Centrale Lyon | Akrout M.,University of Sfax | Fakhfakh T.,University of Sfax | And 2 more authors.
International Journal of Modelling, Identification and Control | Year: 2010

In this paper, we present an inexpensive and robust tool for the vibratory monitoring of cylindrical pipes. The tool will be based on the analysis of the anomalies which affect the elastic waves travelling in the pipe. We develop a numerical approach to study the guided elastic wave propagation in tubular structures. Wave finite element method (WFEM) based on the characterisation of the elastic waves is introduced to investigate the dispersion and wave scattering in pipes. Dynamic reduction technique is employed to improve the computational efficiency. Through WFEM and using a modal decomposition, we develop the dynamical behaviour of the pipe. We study the detection of some defects which affect the junction between two adjacent pipes. The question of the mode sensitivity to the defect's detection is considered. Copyright © 2010 Inderscience Enterprises Ltd.

Danas K.,Laboratoire Of Mecanique Des Solides | Aravas N.,University of Thessaly | Aravas N.,Mechatronics Institute
Composites Part B: Engineering | Year: 2012

A new constitutive model for elasto-plastic (rate-independent) porous materials subjected to general three-dimensional finite deformations is presented. The new model results from simple modifications of an earlier model of Kailasam and Ponte Castañeda (1997, 1998) [40,41] so that it reproduces the exact spherical and cylindrical shell solution (composite sphere and composite cylinder assemblage) under purely hydrostatic loadings, while predicting (by calibration) accurately the void shape evolution according to the recent "second-order" model of Danas and Ponte Castañeda [17]. Furthermore, the present model is based on a rigorous homogenization method which is capable of predicting both the constitutive behavior and the microstructure evolution of porous materials. The microstructure is described by voids of arbitrary ellipsoidal shapes and orientations and as a result the material exhibits deformation-induced (or morphological) anisotropy at finite deformations. This is in contrast with the well-known Gurson [32] model which assumes that the voids remain spherical during the deformation process and thus the material remains always isotropic. The present model is implemented numerically in a finite element program where a three-dimensional thin-sheet (butterfly) specimen is subjected to a combination of shear and traction loading conditions in order to examine the effect of stress triaxiality and shearing upon material failure. The ability of the present model to take into account the nontrivial evolution of the microstructure and especially void shape effects leads to the prediction of material failure even at low stress triaxialities and small porosities without the use of additional phenomenological damage criteria. At high stress triaxialities, the present model gives similar predictions as the Gurson model. © 2011 Elsevier Ltd. All rights reserved.

Danas K.,Laboratoire Of Mecanique Des Solides | Triantafyllidis N.,Laboratoire Of Mecanique Des Solides | Triantafyllidis N.,University of Michigan
Journal of the Mechanics and Physics of Solids | Year: 2014

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. © 2014 Elsevier Ltd. All rights reserved.

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