136 results on '"Mora, Serge"'
Search Results
2. Effects of particle compressibility on structural and mechanical properties of compressed soft granular materials
- Author
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Vu, Thi-Lo, Nezamabadi, Saeid, and Mora, Serge
- Subjects
Condensed Matter - Soft Condensed Matter - Abstract
Changes in the mechanical properties of granular materials, induced by variations in the intrinsic compressibility of the particles, are investigated by means of numerical simulations based on the combination of the Finite Element and Contact Dynamics methods. Assemblies of athermal 2D particles are subjected to quasi-static uni-axial compactions up to packing fractions close to $1$. Inspired by the contact mechanics in the Hertz's limit, we show that the effect of the compressibility of the particles both on the global and the local stresses, can be described by considering only the packing fraction of the system. This result, demonstrated in the whole range of accessible packing fractions in case of frictionless particles, remains relevant for moderate inter-particles coefficients of friction. The small discrepancies observed with frictional particles originate from irreversible local reorganizations in the system, the later being facilitated by the compressibility of the particles.
- Published
- 2020
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3. Cutting and slicing weak solids
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Mora, Serge and Pomeau, Yves
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Condensed Matter - Soft Condensed Matter ,Physics - Fluid Dynamics - Abstract
Dicing soft solids with a sharp knife is quicker and smoother if the blade is sliding rapidly parallel to its edge in addition to the normal squeezing motion. We explain this common observation with a consistent theory suited for soft gels and departing from the standard theories of elastic fracture mechanics developed for a century. The gel is assumed to locally fail when submitted to stresses exceeding a threshold $\sigma_1$. The changes in its structure generate a liquid layer coating the blade and transmitting the stress through viscous forces. The driving parameters are the ratio $U/W$ of the normal to the tangential velocity of the blade, and the characteristic length $\eta W/\sigma_1$, with $\eta$ the viscosity of the liquid. The existence of a maximal value of $U/W$ for a steady regime explains the crucial role of the tangential velocity for slicing biological and other soft materials.
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- 2020
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4. The Shape of Hanging Elastic Cylinders
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Mora, Serge, Ando, Edward, Fromental, Jean-Marc, Phou, Ty, and Pomeau, Yves
- Subjects
Condensed Matter - Soft Condensed Matter - Abstract
Deformations of heavy elastic cylinders with their axis in the direction of earth's gravity field are investigated. The specimens, made of polyacrylamide hydrogels, are attached from their top circular cross section to a rigid plate. An equilibrium configuration results from the interplay between gravity that tends to deform the cylinders downwards under their own weight, and elasticity that resists these distortions. The corresponding steady state exhibits fascinating shapes which are measured with lab-based micro-tomography. For any given initial radius to height ratio, the deformed cylinders are no longer axially symmetric beyond a critical value of a control parameter that depends on the volume force, the height and the elastic modulus: lateral wrinkling hierarchy develops, and holes appear at the bottom surface of the shallowest samples. We show that these patterns are the consequences of elastic instabilities.
- Published
- 2019
5. Impact of beads and drops on a repellent solid surface: a unified description
- Author
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Arora, Sristhti, Fromental, Jean-Marc, Mora, Serge, Phou, Ty, Ramos, Laurence, and Ligoure, Christian
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Condensed Matter - Soft Condensed Matter ,Physics - Fluid Dynamics - Abstract
We investigate freely expanding sheets formed by ultrasoft gel beads, and liquid and viscoelastic drops, produced by the impact of the bead or drop on a silicon wafer covered with a thin layer of liquid nitrogen that suppresses viscous dissipation thanks to an inverse Leidenfrost effect. Our experiments show a unified behaviour for the impact dynamics that holds for solids, liquids, and viscoelastic fluids and that we rationalize by properly taking into account elastocapillary effects. In this framework, the classical impact dynamics of solids and liquids as far as viscous dissipation is negligible, appears as the asymptotic limits of a universal theoretical description. A novel material-dependent characteristic velocity that includes both capillary and bulk elasticity emerges from this unified description of the physics of impact., Comment: to appear in PRL
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- 2018
- Full Text
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6. Rearrangement zone around a crack tip in a double self-assembled transient network
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Foyart, Guillaume, Ligoure, Christian, Mora, Serge, and Ramos, Laurence
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Condensed Matter - Soft Condensed Matter - Abstract
We investigate the nucleation and propagation of cracks in self-assembled viscoelastic fluids, which are made of surfactant micelles reversibly linked by telechelic polymers. The morphology of the micelles can be continuously tuned, from spherical to rod-like to wormlike, thus producing transient double networks when the micelles are sufficiently long and entangled, and transient single networks otherwise. For a single network, we show that cracks nucleate when the sample deformation rate involved is comparable to the relaxation time scale of the network. For a double network, by contrast, significant rearrangements of the micelles occur as a crack nucleates and propagates. We show that birefringence develops at the crack tip over a finite length, $\xi$, which corresponds to the length scale over which micelles alignment occur. We find that $\xi$ is larger for slower cracks, suggesting an increase of ductility., Comment: 10 pages, 4 figures
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- 2016
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7. Effects of particle compressibility on structural and mechanical properties of compressed soft granular materials
- Author
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Vu, Thi-Lo, Nezamabadi, Saeid, and Mora, Serge
- Published
- 2021
- Full Text
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8. Elasto-buoyant heavy spheres: a unique way to test non-linear elasticity
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Chakrabarti, Aditi, Chaudhury, Manoj K., Mora, Serge, and Pomeau, Yves
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Condensed Matter - Materials Science ,Condensed Matter - Soft Condensed Matter - Abstract
Extra-large deformations in ultra-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 ultra-soft elastic medium. We find a scaling law for the penetration depth ($\delta$) of the bead inside the softest gels as $\delta \sim a^{3/2}$. While this result is inconsistent with an ideal neo-Hookean model of elastic deformation, according to which the displacement fields must diverge, it 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 non-linear materials.
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- 2015
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9. Bulk and interfacial stresses in suspensions of soft and hard colloids
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Truzzolillo, Domenico, Roger, Valentin, Dupas, Christelle, Mora, Serge, and Cipelletti, Luca
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Condensed Matter - Soft Condensed Matter - Abstract
We explore the influence of particle softness and internal structure on both the bulk and interfacial rheological properties of colloidal suspensions. We probe bulk stresses by conventional rheology, by measuring the flow curves, shear stress vs strain rate, for suspensions of soft, deformable microgel particles and suspensions of near hard-sphere-like silica particles. A similar behavior is seen for both kind of particles in suspensions at concentrations up to the random close packing volume fraction, in agreement with recent theoretical predictions for sub-micron colloids. Transient interfacial stresses are measured by analyzing the patterns formed by the interface between the suspensions and their own solvent, due to a generalized Saffman-Taylor hydrodynamic instability. At odd with the bulk behavior, we find that microgels and hard particle suspensions exhibit vastly different interfacial stress properties. We propose that this surprising behavior results mainly from the difference in particle internal structure (polymeric network for microgels vs compact solid for the silica particles), rather than softness alone., Comment: 20 pages, 8 figures
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- 2014
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10. Softening of edges of solids by surface tension
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Mora, Serge and Pomeau, Yves
- Subjects
Condensed Matter - Soft Condensed Matter - Abstract
Surface tension tends to minimize the area of interfaces between pieces of matter in different thermodynamic phases, be they in the solid or the liquid state. This can be relevant for the macroscopic shape of very soft solids, and lead to a roughening of initially sharp edges. We calculate this effect for a neo-Hookean elastic solid, with assumptions corresponding to actual experiments, namely the case where an initially sharp edge is rounded by the effect of surface tension felt when the fluid surrounding the soft solid (and so surface tension) is changed at the solid/liquid boundary. We consider two opposite limits where the analysis can be carried to the end, the one of a shallow angle and the one of a very sharp angle. Both cases yield a discontinuity of curvature in the state with surface tension although the initial state had a discontinuous slope.
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- 2014
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11. Gravity driven instability in elastic solids
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Mora, Serge, Phou, Ty, Fromental, Jean-Marc, and Pomeau, Yves
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Condensed Matter - Soft Condensed Matter - Abstract
We demonstrate the instability of the free surface of a soft elastic solid facing downwards. Experiments are carried out using a gel of constant density $\rho$, shear modulus $\mu$, put in a rigid cylindrical dish of depth $h$. When turned upside down, the free surface of the gel undergoes a normal outgoing acceleration $g$. It remains perfectly flat for $\rho g h/\mu<\alpha^* $ with $\alpha^*\simeq 6$, whereas a steady pattern spontaneously appears in the opposite case. This phenomenon results from the interplay between the gravitational energy and the elastic energy of deformation, which reduces the Rayleigh waves celerity and vanishes it at the threshold.
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- 2014
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12. Soft granular matter
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Mora, Serge and Pomeau, Yves
- Subjects
Condensed Matter - Soft Condensed Matter - Abstract
We consider a dilute system of small hard beads or hard fibers immersed in a very soft gel able to withstand large elastic deformations. Because of its low to very low shear modulus, this system is very sensitive to small forces. We calculate the local deformation induced by a constant volume force, the inclusion weight. We explain how this deformation could be put in evidence by using techniques similar to the PIV method (particle image velocimetry) used to show complex velocity fields in transparent fluids.
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- 2014
13. Off-equilibrium surface tension in colloidal suspensions
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Truzzolillo, Domenico, Mora, Serge, Dupas, Christelle, and Cipelletti, Luca
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Condensed Matter - Soft Condensed Matter - Abstract
We study the fingering instability of the interface between two miscible fluids, a colloidal suspension and its own solvent. The temporal evolution of the interface in a Hele-Shaw cell is found to be governed by the competition between the non-linear viscosity of the suspension and an off-equilibrium, effective surface tension $\Gamma_e$. By studying suspensions in a wide range of volume fractions, $\Phi_\mathrm{C}$, we show that $\Gamma_e \sim \Phi_\mathrm{C}^2$, in agreement with Korteweg's theory for miscible fluids. The surface tension exhibits an anomalous increase with particle size, which we account for using entropy arguments., Comment: 5 pages, 5 figures + supplementary material
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- 2013
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14. Effects of the blade shape on the slicing of soft gels
- Author
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Mora, Serge
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- 2021
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15. Synchronous whirling of spinning homogeneous elastic cylinders: linear and weakly nonlinear analyses
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Mora, Serge
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- 2020
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16. Fingering to fracturing transition in a transient gel
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Foyart, Guillaume, Ramos, Laurence, Mora, Serge, and Ligoure, Christian
- Subjects
Condensed Matter - Soft Condensed Matter - Abstract
Fracture processes are ubiquitous in soft materials, even in complex fluids, subjected to stresses. To investigate these processes in a simple geometry, we use a model self-assembled transient gel and study the instability patterns obtained in a radial Hele-Shaw cell when a low viscosity oil pushes the more viscous transient gel. Thanks to an analysis of the morphology of the patterns, we find a discontinuous transition between the standard Saffman-Taylor fingering instability and a fracturing instability as the oil injection rate increases. Our data suggest that the flow properties of the gel ahead of the finger tip controls the transition towards fracturing. By analyzing the displacement field of the gel in the vicinity of the fingers and cracks, we show that in the fingering regime, the oil gently pushes the gel, whereas in the fracturing regime, the crack tears apart the gel, resulting in a strong drop of the gel velocity ahead of the crack tip as compared to the tip velocity. We find a unique behavior for the whole displacement field of a gel around a crack, which is drastically different from that around a finger, and reveals the solid-like behavior of the gel at short time. Our experiments and analysis provide quantitative yet simple tools to unambiguously discriminate a finger from a crack in a visco-elastic material., Comment: to appear in Soft Matter
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- 2013
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17. Fractures in complex fluids: the case of transient networks
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Ligoure, Christian and Mora, Serge
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Condensed Matter - Soft Condensed Matter - Abstract
We present a comprehensive review of the current state of fracture phenomena in transient networks, a wide class of viscoelastic fluids. We will first define what is a fracture in a complex fluid, and recall the main structural and rheological properties of transient networks. Secondly, we review experimental reports on fractures of transient networks in several configurations: shear-induced fractures, fractures in Hele-Shaw cells and fracture in extensional geometries (filament stretching rheometry and pendant drop experiments), including fracture propagation. The tentative extension of the concepts of brittleness and ductility to the fracture mechanisms in transient networks is also discussed. Finally, the different and apparently contradictory theoretical approaches developed to interpret fracture nucleation will be addressed and confronted to experimental results. Rationalized criteria to discriminate the relevance of these different models will be proposed., Comment: Review; Rheologica Acta 2013 published on line
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- 2013
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18. Buckling of a compliant hollow cylinder attached to a rotating rigid shaft
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Mora, Serge and Richard, Franck
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- 2019
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19. Microemulsion nanocomposites: phase diagram, rheology and structure using a combined small angle neutron scattering and reverse Monte Carlo approach
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Puech, Nicolas, Mora, Serge, Phou, Ty, Porte, Gregoire, Jestin, Jacques, and Oberdisse, Julian
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Condensed Matter - Soft Condensed Matter - Abstract
The effect of silica nanoparticles on transient microemulsion networks made of microemulsion droplets and telechelic copolymer molecules in water is studied, as a function of droplet size and concentration, amount of copolymer, and nanoparticle volume fraction. The phase diagram is found to be affected, and in particular the percolation threshold characterized by rheology is shifted upon addition of nanoparticles, suggesting participation of the particles in the network. This leads to a peculiar reinforcement behaviour of such microemulsion nanocomposites, the silica influencing both the modulus and the relaxation time. The reinforcement is modelled based on nanoparticles connected to the network via droplet adsorption. Contrast-variation Small Angle Neutron Scattering coupled to a reverse Monte Carlo approach is used to analyse the microstructure. The rather surprising intensity curves are shown to be in good agreement with the adsorption of droplets on the nanoparticle surface.
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- 2010
20. Selection of hexagonal buckling patterns by the elastic Rayleigh-Taylor instability
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Chakrabarti, Aditi, Mora, Serge, Richard, Franck, Phou, Ty, Fromental, Jean-Marc, Pomeau, Yves, and Audoly, Basile
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- 2018
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21. Structure and rheological properties of model microemulsion networks filled with nanoparticles
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Puech, Nicolas, Mora, Serge, Testard, Vincent, Porte, Grégoire, Ligoure, Christian, Grillo, Isabelle, Phou, Ty, and Oberdisse, Julian
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Condensed Matter - Soft Condensed Matter - Abstract
Model microemulsion networks of oil droplets stabilized by non ionic surfactant and telechelic polymer C18-PEO(10k)-C18 have been studied for two droplet-to-polymer size ratios. The rheological properties of the networks have been measured as a function of network connectivity and can be described in terms of simple percolation laws. The network structure has been characterised by Small Angle Neutron Scattering. A Reverse Monte Carlo approach is used to demonstrate the interplay of attraction and repulsion induced by the copolymer. These model networks are then used as matrix for the incorporation of silica nanoparticles (R=10nm), individual dispersion being checked by scattering. A strong impact on the rheological properties is found for silica volume fractions up to 9%.
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- 2008
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22. Buckling of a spinning elastic cylinder : linear, weakly nonlinear and post-buckling analyses
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Richard, Franck, Chakrabarti, Aditi, Audoly, Basile, Pomeau, Yves, and Mora, Serge
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- 2018
23. Rheology of soft granular materials: uniaxial compression
- Author
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Nezamabadi Saeid, Radjai Farhang, Mora Serge, Delenne Jean-Yves, and Ghadiri Mojtaba
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Physics ,QC1-999 - Abstract
Soft granular materials are assemblies of highly deformable grains interacting via surface forces. The large grain deformations of these materials differ them from hard granular systems, in which, their behaviors are essentially governed by grain rearrangements. In this paper, we study the uniaxial compression of soft granular materials using a numerical approach based on the Material Point Method allowing for large grain deformations, coupled with the Contact Dynamics method for the treatment of unilateral frictional contacts between grains. Considering the neo-Hookean and elasto-plastic grains, the compaction of 2D soft granular packings is analyzed. We focus essentially on the evolution of the packing vertical stress as a function of the packing fraction and the predictive models are proposed.
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- 2021
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24. In situ X-ray CT imaging of transient water retention experiments with cyclic drainage and imbibition
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Milatz, Marius, primary, Andò, Edward, additional, Viggiani, Gioacchino, additional, and Mora, Serge, additional
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- 2022
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25. Highly deformed grain: from the Hertz contact limitation to a new strain field description in 2D
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Mora Serge, Vu Thi-Lo, Barés Jonathan, and Nezamabadi Saeid
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Physics ,QC1-999 - Abstract
Most of the 2D studies on granular materials consider an assembly of cylindrical particles in the small deformation regime. Investigating the range of validity of the small deformation hypothesis is therefore of crucial importance in order to determine the quantitative relevance of the predictions emerging from these 2D studies. We introduce here a novel experimental set-up based on high resolution imaging and image correlation, and capable of measuring the strain field inside the particles with a cutting edge accuracy. We measure the strain field inside a unique circular cylindrical elastic particle undergoing an uniaxial compression. The significant deviations arising from the comparison with the predictions of the small deformation limit predicted by the Hertz’s theory, and numerical simulations, give insight to improve the modeling of 2D granular materials.
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- 2017
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26. Experimental observations of root growth in a controlled photoelastic granular material
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Barés Jonathan, Mora Serge, Delenne Jean-Yves, and Fourcaud Thierry
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Physics ,QC1-999 - Abstract
We present a novel root observation apparatus capable of measuring the mechanical evolution of both the root network and the surrounding granular medium. The apparatus consists of 11 parallel growth frames, two of them being shearable, where the roots grow inside a photo-elastic or glass granular medium sandwiched between two pieces of glass. An automated system waters the plant and image each frame periodically in white light and between crossed polarisers. This makes it possible to follow (i) the root tips and (ii) the grain displacements as well as (iii) their inner pressure. We show how a root networks evolve in a granular medium and how it can mechanically stabilize it. This constitutes a model experiment to move forward in the understanding of the complex interaction between root growth and surrounding soil mechanical evolution.
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- 2017
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27. Analysis of dense packing of highly deformed grains
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Vu Thi Lo, Nezamabadi Saeid, Barés Jonathan, and Mora Serge
- Subjects
Physics ,QC1-999 - Abstract
This paper concerns modeling of soft granular materials in which the grains are highly deformable. In order to simulate these materials, an approach based on an implicit formulation of the Material Point Method in the context of the finite strain theory, allowing for large deformations of grains, coupled with the Contact Dynamics method for the treatment of unilateral frictional contacts between grains, is proposed. In this context, the Mooney-Rivlin constitutive relationship is applied with two different set of elastic parameters. Considering these two material behaviors, a uniaxial compression of 2D soft granular packings is analyzed. The stress-strain relation and the evolution of the packing fraction as well as of the connectivity of the grains are discussed.
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- 2017
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28. Compaction rheology of soft granular materials
- Author
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Nezamabadi, Saeid, Nguyen, Thanh Hai, Vu, Thi Lo, Mora, Serge, Delenne, Jean-Yves, Radjai, Farhang, Laboratoire de Mécanique et Génie Civil (LMGC), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Physique et Mécanique des Milieux Divisés (PMMD), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Ingénierie des Agro-polymères et Technologies Émergentes (UMR IATE), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université de Montpellier (UM)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), and Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Université Montpellier 2 - Sciences et Techniques (UM2)
- Subjects
[SPI.FLUID]Engineering Sciences [physics]/Reactive fluid environment ,[SPI.GPROC]Engineering Sciences [physics]/Chemical and Process Engineering ,[PHYS.MECA]Physics [physics]/Mechanics [physics] ,ComputingMilieux_MISCELLANEOUS ,[SPI.MAT]Engineering Sciences [physics]/Materials - Abstract
International audience
- Published
- 2020
29. Cutting and Slicing Weak Solids
- Author
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Mora, Serge, primary and Pomeau, Yves, additional
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- 2020
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30. Spinning elastic beads: a route for simultaneous measurements of the shear modulus and the interfacial energy of soft materials
- Author
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Carbonaro, Alessandro, primary, Chagua-Encarnacion, Kennedy-Nexon, additional, Charles, Carole-Ann, additional, Phou, Ty, additional, Ligoure, Christian, additional, Mora, Serge, additional, and Truzzolillo, Domenico, additional
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- 2020
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31. Compaction of elastic granular materials: inter-particles friction effects and plastic events
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Vu, Thi-Lo, primary, Nezamabadi, Saeid, additional, and Mora, Serge, additional
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- 2020
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32. Impact of elastic beads and liquid drops on repellent surface :a unified description
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Arora, Srishti, FROMENTAL, Jean-marc, Mora, Serge, PHOU, Ty, RAMOS, Laurence, LIGOURE, Christian, Laboratoire Charles Coulomb (L2C), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Physique et Mécanique des Milieux Divisés (PMMD), Laboratoire de Mécanique et Génie Civil (LMGC), and Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)
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Condensed Matter::Soft Condensed Matter ,Physics::Fluid Dynamics ,[PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph] ,[PHYS.COND.CM-SCM]Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft] - Abstract
International audience; We investigate freely expanding sheets formed by ultrasoft gel beads, and liquid and viscoelastic drops, produced by the impact of the bead or drop on a silicon wafer covered with a thin layer of liquid nitrogen that suppresses viscous dissipation thanks to an inverse Leidenfrost effect. Our experiments show a unified behavior for the impact dynamics that holds for solids, liquids, and viscoelastic fluids and that we rationalize by properly taking into account elastocapillary effects. In this framework, the classical impact dynamics of solids and liquids, as far as viscous dissipation is negligible, appears as the asymptotic limits of a universal theoretical description. A novel material-dependent characteristic velocity that includes both capillary and bulk elasticity emerges from this unified description of the physics of impact.
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- 2018
33. Numerical simulations of the compaction of assemblies of rubberlike particles: A quantitative comparison with experiments
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Vu, Thi-Lo, primary, Barés, Jonathan, additional, Mora, Serge, additional, and Nezamabadi, Saeid, additional
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- 2019
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34. A meniscus fingering instability in viscoelastic fluids
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Saintyves, Baudouin, primary, Mora, Serge, additional, and Bouchaud, Elisabeth, additional
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- 2019
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35. The shape of hanging elastic cylinders
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Mora, Serge, primary, Andò, Edward, additional, Fromental, Jean-Marc, additional, Phou, Ty, additional, and Pomeau, Yves, additional
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- 2019
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36. Brownian diffusion in a dilute field of traps is Fickean but non-Gaussian
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Mora, Serge, primary and Pomeau, Yves, additional
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- 2018
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37. Stress relaxation in model transient networks: percolation and rearrangement of the crosslinks
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Filali, Mohammed, Michel, Eric, Mora, Serge, Molino, François, and Porte, Grégoire
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- 2001
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38. Contact entre particules déformables : de la limite de Hertz aux grandes déformations
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Vu, Thi, Lo, Mora, Serge, NEZAMABADI, Saeid, Barés, Jonathan, and Association Française de Mécanique
- Subjects
Corrélations d'images numériques ,méthode ,élément finis ,[PHYS.MECA]Physics [physics]/Mechanics [physics] ,hyperélasticité ,contact - Abstract
Colloque avec actes et comité de lecture. Internationale.; International audience; La plupart des études bidimensionnelles sur les matériaux granulaires considèrent l'assemblage de particules cylindriques dans le régime des petites déformations, en utilisant la description du contact de Hertz. Néanmoins, dans plusieurs cas, les déformations subies par les particules ne sont pas infinitésimales. L'étude de validité de l'hypothèse des petites déformations représente donc un enjeu important pour déterminer la pertinence des prévisions issues de ces études bidimensionnelles. Au moyen de nouvelles approches expérimentales, nous étudions la déformation d'un assemblage de particules soumis à grandes déformations. Nous avons mis en place un appareil expérimental capable de comprimer ou de cisailler un assemblage de particules, couplé à un dispositif d'imagerie à haute résolution (taille de pixel est 5.29 ?m) pour obtenir des images de chaque particule au cours d'un chargement. La mesure du champs de déformation et son évolution sont obtenues par la corrélation d'images numériques, et plusieurs paramètres ont été pris en compte tels que le frottement entre particules et la polydispersité de taille. Parallèlement à ces expériences, des simulations numériques sont réalisées dans les mêmes conditions à l'aide de la méthode des éléments finis et de la méthodes des points matériels [1]. Cette dernière méthode est basée sur la discrétisation de chaque particule par une collection de point matériels. L'information portée par les points matériels est projetée sur un maillage de fond, où les équations du mouvement sont résolues. Cette solution est alors utilisée pour mettre à jour les points matériels. Différents grandeurs macroscopiques (contrainte, compacité...) et microscopiques (connectivité, anisotropie...) sont obtenues numériquement et expérimentalement. Une comparaison entre ces paramètres numériques et expérimentaux permet de valider mutuellement ces approches et de déterminer le comportement de ces matériaux à particules déformables. REFERENCES [1] S. Nezamabadi et al., Implicit frictional-contact model for soft particle systems, Journal of Mechanics and Physics Solids, 2015
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- 2017
39. 3D geometry of hyperelastic hydrogels studied with fast x-ray tomography
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Andò, Edward, PHOU, Ty, FROMENTAL, Jean-marc, Mora, Serge, Laboratoire sols, solides, structures - risques [Grenoble] (3SR ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Laboratoire Charles Coulomb (L2C), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Chimie et Matériaux, Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Mécanique et Génie Civil (LMGC), and Physique et Mécanique des Milieux Divisés (PMMD)
- Subjects
x-ray tomography ,geometry ,fast tomography ,hydrogel ,[PHYS.COND.CM-SCM]Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft] ,[SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing ,[SPI.MAT]Engineering Sciences [physics]/Materials - Abstract
International audience; In this paper we present geometrical measurements made on aqueous polyacrylamide gels withlab-based micro-tomography, one of the most convenient ways of accessing a quantitative measurement of thefascinating shapes that these materials make when hanging under their own weight.
- Published
- 2017
40. Impact of solid and liquid balls on a solid surface: an unified description
- Author
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ARORA, Srishti, FROMENTAL, Jean-marc, Mora, Serge, PHOU, Ty, RAMOS, Laurence, LIGOURE, Christian, Laboratoire Charles Coulomb (L2C), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Mécanique et Génie Civil (LMGC), Physique et Mécanique des Milieux Divisés (PMMD), and Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Physics::Fluid Dynamics ,[PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph] ,[PHYS.COND.CM-SCM]Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft] - Abstract
International audience; We study experimentally the impact of ultra soft spherical gel balls of millimetric size d0 on a rigid substrate covered by a thin layer of liquid nitrogen to avoid viscous dissipation .The balls largely deform like a pancake at high impact velocities. We measure the maximally deformed size dmax and the the time needed to reach this maximal size after impact Tmax, versus the impact velocity Ui for various elastic moduli . We do the same type of experiments with liquid droplets of various surface tensions . The experiments reveal a universal scaling behavior of the maximum deformation $\d_{max}/d_0}$ of both solid balls and liquid drops provided that both bulk and surface elasticity are properly taken into account. Moreover, we show that , in absence of viscous dissipation, the dynamics of the system can be understood as a conventional spring-mass system with a stiffness given by a combination of surface tension and bulk elasticity and a mass given by that of the ball (or drop) ; the deformation of the small ball (drop) during the impact linearly depends on the impact velocity, and the contact time scales as the period of this spring-mass system.
- Published
- 2017
41. Non-equilibrium interfacial tension in simple and complex fluids
- Author
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TRUZZOLILLO, Domenico, Mora, Serge, Dupas, Christelle, CIPELLETTI, Luca, Laboratoire Charles Coulomb (L2C), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Physique et Mécanique des Milieux Divisés (PMMD), Laboratoire de Mécanique et Génie Civil (LMGC), and Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)
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Physics::Fluid Dynamics ,Condensed Matter::Soft Condensed Matter ,[PHYS.COND.CM-SCM]Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft] - Abstract
International audience; In our work we report the measurement of non-equilibrium interfacial tension of polymer and hard sphere suspensions in contact with their own solvent. By visualizing fingering instability (VF) in radial Hele-Shaw geometry, appearing when the solvent displaces suspensions of colloids or polymers, we measure interfacial tensions in function of the volume fraction of the suspended objects, showing that the internal degrees of freedom of the particles drive the low volume fraction behavior (Figure 1). Our results support the existence of a positive tension between miscible fluids, confirm the quadratic scaling predicted by Korteweg [4] for long linear and crosslinked polymers and show a positive rapidly growing tension for hard sphere suspensions up to maximum packing, whose description necessitates a theoretical framework going beyond the classic square gradient model. We rationalize our findings assuming the suspension/solvent interface in local thermodynamic equilibrium, computing explicitly the square gradient contribution to the interfacial tension for polymer/solvent and simple molecular liquid mixtures and proposing a phenomenological model capturing the compositional dependence of the interfacial tension for large concentration gradients. Finally we include and analyze data reported in literature and obtained via spinning drop tensiometry that validate the model and we propose the analysis of fluid dynamic instability as a new tool to probe interfacial stresses.
- Published
- 2017
42. Souple et solide : comment la matière élastique se déforme-t-elle ?
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Mora, Serge, primary and Pomeau, Yves, additional
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- 2017
- Full Text
- View/download PDF
43. Off-equilibrium surface tension in driven colloidaland polymer suspensions
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TRUZZOLILLO, Domenico, CIPELLETTI, Luca, Dupas, Christelle, Mora, Serge, Laboratoire Charles Coulomb (L2C), and Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Physics::Fluid Dynamics ,Condensed Matter::Soft Condensed Matter ,[PHYS.COND.CM-SCM]Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft] - Abstract
We report the measurement of non-equilibrium interfacial tension of polymer and hard sphere suspensions in contact with their own solvent. By visualizing fingering instability (VF) in radial Hele-Shaw geometry, we measure interfacial tension in function of the volume fraction of the suspensions showing that the internal degrees of freedom of the particles drive the magnitude of such tension. We rationalize our findings proposing a phenomenological model capturing the compositional dependence of the non equilibrium interfacial tension for the whole range of concentration gradients and for all the systems at hand. More generally we propose the analysis of fluid dynamic instabilities as a new tool to measure interfacial tensions between complex fluids.
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- 2016
44. Off-equilibrium surface tension in driven colloidal and polymer suspensions
- Author
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TRUZZOLILLO, Domenico, CIPELLETTI, Luca, DUPAS, Christelle, Mora, Serge, Laboratoire Charles Coulomb (L2C), and Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)
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Physics::Fluid Dynamics ,Condensed Matter::Soft Condensed Matter ,[PHYS.COND.CM-SCM]Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft] - Abstract
The nature of the interface between two fluids has been the subject of an extensive investigation for more than two centuries [1]. From a mechanical point of view, surface tension can be calculated as an integral of unbalanced tangential stresses over the interface thickness [2] and it is thus of no surprise that, within the assumption of temporal and local equilibrium, such a tension can be ascribed to an interface between two miscible fluids [3] and assumes a nonzero value. The idea that there are capillary forces at work in the layer between miscible liquids goes back at least to an 1871 report of J. Bosscha, cited in a paper of Korteweg [1901], who was the first [4] to introduce stresses due to concentration inhomogeneities in the Navier-Stokes equation, aiming to mimic capillarity effects between two miscible liquids. Only much more recently experimental effort has been made to investigate the existence and the nature (the sign) of such off-equilibrium tension [5-11]. In all cases the authors have pointed out that such interfacial stresses mimic a positive interfacial tension. In analogy with the surface tension of an equilibrium interface between immiscible fluids, the effective surface tension has been rationalized within an approximation of small concentration gradients via the so called square gradient model [6,8,9]. The latter predicts a quadratic dependence of such tension on the compositional mismatch between two miscible fluids.Only very recently colloids and polymer suspensions in contact with a reservoir of solvent have been considered as a model two-fluid system to study off-equilibrium surface tensions [11, 12]: indeed, diffusion is much slower in colloids and polymers as compared to atomic systems, leaving a wider temporal window for probing the transient interface between miscible fluids. In a recent work [11] we have investigated off-equilibrium surface tension between microgel suspensions and their solvent (water) showing that equation (1) holds for low concentration gradients. On the other hand we have also pointed out that the square gradient model is far to catch the volume fraction dependence of the tension for compact hard sphere-like particles [12] up to concentrations close to the maximum packing for spheres. The scenario is then currently controversial.By visualizing viscous fingering instability (VF), appearing when a solvent displaces a suspension in radial Hele-Shaw geometry, we measure interfacial tensions in function of the volume fraction of the suspended colloids or polymers, showing that the internal degrees of freedom of the particles drive the low volume fraction behavior. Our results support the existence of a positive tension between miscible fluids, confirm the quadratic scaling predicted by Korteweg [4] for long linear and crosslinked polymers and show a positive rapidly growing tension for hard sphere suspensions, whose description necessitates a theoretical framework going beyond the classic square gradient model. We rationalize our findings assuming the suspension/solvent interface in local thermodynamic equilibrium, computing explicitly the square gradient contribution to the interfacial tension for polymer/solvent and simple molecular liquid mixtures and proposing a new phenomenological model capturing the compositional dependence of the interfacial tension for large concentration gradients. In addition to that we include and analyze data reported in literature and obtained via spinning drop tensiometry, validating our approach. We conclude proposing very generally the analysis of hydrodynamic instabilities as a new tool to measure interfacial stresses in complex fluids and characterize transient interfacial tensions.
- Published
- 2016
45. Off-equilibrium surface tension in colloidal and polymer suspensions
- Author
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TRUZZOLILLO, Domenico, DUPAS, Christelle, Mora, Serge, CIPELLETTI, Luca, Laboratoire Charles Coulomb (L2C), and Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)
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[PHYS.COND.CM-SCM]Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft] - Abstract
International audience; Surface tension between immiscible fluids is a well-understood and well-characterized phenomenon. By contrast, much less is known about the effective, off-equilibrium surface tension that arises when a (transient) interface is created between miscible fluids.This effective surface tension plays a key role in many driven phenomena, from jetting and drop formation and coalescence to precipitation and deposition, as it was already recognized more than 100 years ago by Korteweg [1]. However, experimental investigations in this field remain scarce and the theoretical predictions by Korteweg have not quantitatively tested so far, to the best of our knowledge. We present a thorough experimental investigation of the Saffman-Taylor instability arising when a simple fluid (the solvent of a colloidal or polymer suspension) is pushed through a miscible, more viscous one (the colloidal or polymer suspension itself). We show [2] that the resulting interface pattern can be accounted for by the non-linear rheological properties of the suspension and an effective surface tension. By measuring the effective surface tension for suspensions at a variety of polymer volume fractions, we successfully test Korteweg's theory for free and cross-linked polymer suspensions. We moreover find that the effective surface tension increases with the size of polymers, a surprising result at odd with the typical behavior in atomic or colloidal systems at equilibrium, where the surface tension usually decreases as the squared particle size. Finally we present new data on the effective surface tension between suspensions of hard, compact particles and their own solvent showing that polymers and hard particles exhibit vastly different effective surface tension properties. We discuss this surprising result in view of available models for interfacial stresses.[1] D. Korteweg, Arch. Neerlandaises Sci. Exactes Naturelles, 6, 1 (1901).[2] D.Truzzolillo, S. Mora, C. Dupas, L. Cipelletti, Phys. Rev. Lett., 112, 208303 (2014).
- Published
- 2015
46. Elastobuoyant Heavy Spheres: A Unique Way to Study Nonlinear Elasticity
- Author
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Chakrabarti, Aditi, primary, Chaudhury, Manoj K., additional, Mora, Serge, additional, and Pomeau, Yves, additional
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- 2016
- Full Text
- View/download PDF
47. Nonequilibrium Interfacial Tension in Simple and Complex Fluids
- Author
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Truzzolillo, Domenico, primary, Mora, Serge, additional, Dupas, Christelle, additional, and Cipelletti, Luca, additional
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- 2016
- Full Text
- View/download PDF
48. Rearrangement Zone around a Crack Tip in a Double Self-Assembled Transient Network
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Foyart, Guillaume, primary, Ligoure, Christian, additional, Mora, Serge, additional, and Ramos, Laurence, additional
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- 2016
- Full Text
- View/download PDF
49. Analysis of dense packing of highly deformed grains.
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Thi Lo Vu, Nezamabadi, Saeid, Barés, Jonathan, and Mora, Serge
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GRANULAR materials ,PACKING (Mechanical engineering) ,DEFORMATIONS (Mechanics) ,STRAINS & stresses (Mechanics) ,FRICTION ,COMPRESSION loads - Abstract
This paper concerns modeling of soft granular materials in which the grains are highly deformable. In order to simulate these materials, an approach based on an implicit formulation of the Material Point Method in the context of the finite strain theory, allowing for large deformations of grains, coupled with the Contact Dynamics method for the treatment of unilateral frictional contacts between grains, is proposed. In this context, the Mooney-Rivlin constitutive relationship is applied with two different set of elastic parameters. Considering these two material behaviors, a uniaxial compression of 2D soft granular packings is analyzed. The stress-strain relation and the evolution of the packing fraction as well as of the connectivity of the grains are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
50. Tiges capillaires
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Mora, Serge, PISMEN, Len, Pomeau, Yves, Association Française de Mécanique, and Service irevues, irevues
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colonnes ,profils creux en acier ,résistance au feu ,constructions mixtes acier-béton ,[PHYS.MECA]Physics [physics]/Mechanics [physics] ,[PHYS.MECA] Physics [physics]/Mechanics [physics] - Abstract
Colloque avec actes et comité de lecture. Internationale.; International audience; Nous montrons qu'une tige élastique incompressible entièrement plongée dans un liquide se déforme sous l'effet de forces capillaires. Suivant les propriétés de symétrie de la section, trois modes de déformation sont possibles : (i) un cylindre circulaire est comprimé axialement, tandis que sa section de dilate de façon homogène ; (ii) Les arêtes vives d'une tige parallélépipédique carrée s'arrondissent, de telle sorte que les sections tendent vers la forme circulaire ; (iii) un prisme triangulaire à base non-équilatérale se courbe. Pour tous ces modes, nous comparons des expériences à des simulations numériques avec un bel accord quantitatif. Ceci met en évidence le couplage qui existe entre la réponse élastique d'un solide mou et les forces capillaires agissant à l'interface solide-liquide. S. Mora, C. Maurini, T. Phou, J.M. Fromental, B. Audoly et Y. Pomeau, 'Capillary deformations of soft immersed rods', soumis à Phys. Rev. Lett. (2013)
- Published
- 2013
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