CNRS Mechanical and Civil Engineering Laboratory

Montpellier, France

CNRS Mechanical and Civil Engineering Laboratory

Montpellier, France
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Truzzolillo D.,CNRS Charles Coulomb Laboratory | Mora S.,CNRS Mechanical and Civil Engineering Laboratory | Dupas C.,CNRS Charles Coulomb Laboratory | Cipelletti L.,CNRS Charles Coulomb Laboratory
Physical Review X | Year: 2016

Interfacial tension between immiscible phases is a well-known phenomenon, which manifests itself in everyday life, from the shape of droplets and foam bubbles to the capillary rise of sap in plants or the locomotion of insects on a water surface. More than a century ago, Korteweg generalized this notion by arguing that stresses at the interface between two miscible fluids act transiently as an effective, nonequilibrium interfacial tension, before homogenization is eventually reached. In spite of its relevance in fields as diverse as geosciences, polymer physics, multiphase flows, and fluid removal, experiments and theoretical works on the interfacial tension of miscible systems are still scarce, and mostly restricted to molecular fluids. This leaves crucial questions unanswered, concerning the very existence of the effective interfacial tension, its stabilizing or destabilizing character, and its dependence on the fluid's composition and concentration gradients. We present an extensive set of measurements on miscible complex fluids that demonstrate the existence and the stabilizing character of the effective interfacial tension, unveil new regimes beyond Korteweg's predictions, and quantify its dependence on the nature of the fluids and the composition gradient at the interface. We introduce a simple yet general model that rationalizes nonequilibriuminterfacial stresses to arbitrary mixtures, beyond Korteweg's small gradient regime, and show that the model captures remarkably well both our new measurements and literature data on molecular and polymer fluids. Finally,we briefly discuss the relevance of our model to a variety of interface-driven problems, from phase separation to fracture, which are not adequately captured by current approaches based on the assumption of small gradients.


Chakrabarti A.,Lehigh University | Chaudhury M.K.,Lehigh University | Mora S.,CNRS Mechanical and Civil Engineering Laboratory | Pomeau Y.,University of Arizona
Physical Review X | Year: 2016

Large deformations in soft elastic materials are ubiquitous, yet systematic studies and methods to understand the mechanics of such huge strains are lacking. Here, we investigate this complex problem systematically with a simple experiment: by introducing a heavy bead of radius a in an incompressible soft elastic medium. We find a scaling law for the penetration depth (δ) of the bead inside the softest gels as δ ~ a3/2, which is vindicated by an original asymptotic analytic model developed in this article. This model demonstrates that the observed relationship is precisely at the demarcating boundary of what would be required for the field variables to either diverge or converge. This correspondence between a unique mathematical prediction and the experimental observation ushers in new insights into the behavior of the deformations of strongly nonlinear materials.


Michaille G.,French National Center for Scientific Research | Nait-Ali A.,CNRS Mechanical and Civil Engineering Laboratory | Pagano S.,French National Center for Scientific Research
Applied Mathematics Research eXpress | Year: 2014

By using ergodic theory of subadditive processes and variational convergence, we study the macroscopic behavior of a thin 3D composite made up of high-conductivity fibers that are randomly distributed according to a stochastic point process in a bounded open set of. The thickness of the body, the conductivity and the size of the cross sections of the fibers depend on a small parameter ε. The variational limit functional energy obtained when ε tends to 0 is deterministic and depends on two variables: one is the solution of a variational problem posed in a 2D bounded open set and describes the behavior of the medium; the other captures the limit behavior of suitably rescaled solutions in the fibers when the thickness and the size section become increasingly thin and the conductivity of the fibers becomes increasingly large. © 2013 The Author(s) 2013. Published by Oxford University Press. All rights reserved. For permissions, please.


Hafsa O.,University of Nimes | Hafsa O.,CNRS Mechanical and Civil Engineering Laboratory | Mandallena J.-P.,University of Nimes
Journal of Convex Analysis | Year: 2012

We give an overview of relaxation and 3d-2d passage theorems in hyperelasticity in the framework of the multidimensional calculus of variations. We give several improvements of the proofs and we introduce the concept of p-ample integrand in showing its interest with respect to determinant type constraints. Some open questions are addressed. © Heldermann Verlag.


Augier F.,French Institute of Petroleum | Idoux F.,French Institute of Petroleum | Delenne J.Y.,CNRS Mechanical and Civil Engineering Laboratory
Chemical Engineering Science | Year: 2010

In this study, we investigate the transport and transfer properties inside packed beds of spherical particles by means of CFD simulations. Heat and mass transfer properties have been computed in packing configurations of increasing complexity at low to moderate Reynolds numbers (1


Malachanne E.,Ecole des Mines d'Ales | Dureisseix D.,CNRS Contacts and Structural Mechanics Laboratory | Jourdan F.,CNRS Mechanical and Civil Engineering Laboratory
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2011

In this article, a phenomenological numerical model of bone remodeling is proposed. This model is based on the poroelasticity theory in order to take into account the effects of fluid movements in bone adaptation. Moreover, the proposed remodeling law is based on the classical 'Stanford' law, enriched in order to take into account the loading frequency, through fluid movements. This coupling is materialized by a quadratic function of Darcy velocity. The numerical model is carried out, using a finite element method, and calibrated using experimental results at macroscopic level, from the literature. First results concern cyclic loadings on a mouse ulna, at different frequencies between 1Hz and 30Hz, for a force amplitude of 1.5N and 2N. Experimental results exhibit a sensitivity to the loading frequency, with privileged frequency for bone remodeling between 5Hz and 10Hz, for the force amplitude of 2N. For the force amplitude of 1.5N, no privileged frequencies for bone remodeling are highlighted. This tendency is reproduced by the proposed numerical computations. The model is identified on a single case (one frequency and one force amplitude) and validated on the other ones. The second experimental validation deals with a different loading regime, an internal fluid pressure at 20Hz on a turkey ulna. The same framework is applied, and the numerical and experimental data are still matching in terms of gain in bone mass density. © 2011 Elsevier Ltd.


Dresp-Langley B.,CNRS Mechanical and Civil Engineering Laboratory | Reeves A.,Northeastern University
Seeing and Perceiving | Year: 2012

We show that true colors as defined by Chevreul (1839) produce unsuspected simultaneous brightness induction effects on their immediate grey backgrounds when these are placed on a darker (black) general background surrounding two spatially separated configurations. Assimilation and apparent contrast may occur in one and the same stimulus display. We examined the possible link between these effects and the perceived depth of the color patterns which induce them as a function of their luminance contrast. Patterns of square-shaped inducers of a single color (red, green, blue, yellow, or grey) were placed on background fields of a lighter and a darker grey, presented on a darker screen. Inducers were always darker on one side of the display and brighter on the other in a given trial. The intensity of the grey backgrounds varied between trials only. This permitted generating four inducer luminance contrasts, presented in random order, for each color. Background fields were either spatially separated or consisted of a single grey field on the black screen. Experiments were run under three environmental conditions: dark-adaptation, daylight, and rod-saturation after exposure to bright light. In a first task, we measured probabilities of contrast, assimilation, and no effect in a three-alternative forced-choice procedure (background appears brighter on the 'left', on the 'right' or the 'same'). Visual adaptation and inducer contrast had no significant influence on the induction effects produced by colored inducers. Achromatic inducers produced significantly stronger contrast effects after dark-adaptation, and significantly stronger assimilation in daylight conditions. Grouping two backgrounds into a single one was found to significantly decrease probabilities of apparent contrast. Under the same conditions, we measured probabilities of the inducers to be perceived as nearer to the observer (inducers appear nearer on 'left', on 'right' or the 'same'). These, as predicted by Chevreul's law of contrast, were determined by the luminance contrast of the inducers only, with significantly higher probabilities of brighter inducers to be seen as nearer, and a marked asymmetry between effects produced by inducers of opposite sign. Implications of these findings for theories which attempt to link simultaneous induction effects to the relative depth of object surfaces in the visual field are discussed. © 2012 Koninklijke Brill NV, Leiden.


Mutabaruka P.,CNRS Mechanical and Civil Engineering Laboratory | Delenne J.-Y.,Montpellier University | Soga K.,University of Cambridge | Radjai F.,Montpellier University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ≃0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the fluid on the granular microstructure. © 2014 American Physical Society.


Bellieud M.,CNRS Mechanical and Civil Engineering Laboratory
Archive for Rational Mechanics and Analysis | Year: 2012

We study a notion of capacity related to elasticity which proves convenient for analyzing the concentrations of strain energy caused by rigid displacements of some infinitesimal parts of an elastic body in two or three dimensions. By way of application, we investigate the behavior of solutions to initial boundary value problems describing vibrations of periodic elastic composites with rapidly varying elastic properties. More specifically, we analyze a two-phase medium whereby a set of heavy stiff tiny particles is embedded in a softer matrix. This task is set in the context of linearized elasticity. © 2011 Springer-Verlag.


Anza Hafsa O.,CNRS Mechanical and Civil Engineering Laboratory
ESAIM - Control, Optimisation and Calculus of Variations | Year: 2010

We study the integral representation of relaxed functionals in the multi-dimensional calculus of variations, for integrands which are finite in a convex bounded set with nonempty interior and infinite elsewhere. © 2008 EDP Sciences, SMAI.

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