AZEMA Emilien
Organisme : Université Montpellier
Maître de ConférencesDirecteur(trice) de thèse de :
CARDENAS M.,
emilien.azema
umontpellier.fr
0467149711
Bureau: 110, Etg: 1, Bât: 2  Site : SaintPriest
Domaines de Recherche:  Sciences de l'ingénieur/Mécanique/Mécanique des matériaux
 Sciences de l'ingénieur/Mécanique/Mécanique des solides
 Physique/Mécanique
 Physique/Matière Condensée
 Physique/Matière Condensée/Matière Molle
 Sciences de l'ingénieur/Matériaux
 Sciences du Vivant
 Sciences de l'ingénieur/Mécanique/Matériaux et structures en mécanique
 Sciences de l'ingénieur/Génie civil/Géotechnique
 Sciences de l'ingénieur/Mécanique/Mécanique des structures
 Physique/Matière Condensée/Systèmes désordonnés et réseaux de neurones
 Physique/Matière Condensée/Electrons fortement corrélés
 Physique/Physique/Physique Atomique
 Physique/Mécanique/Mécanique des solides
 Physique/Mécanique/Mécanique des matériaux
 Sciences de l'ingénieur/Mécanique/Mécanique des fluides
 Physique/Mécanique/Matériaux et structures en mécanique
 Physique/Mécanique/Mécanique des structures
 Sciences de l'ingénieur/Mécanique/Génie mécanique
 Physique/Mécanique/Génie mécanique
 Sciences de l'ingénieur

Dernieres productions scientifiques :


Scaling in Cohesive Selfgravitating Aggregates
Auteur(s): Sánchez Paul, Azema E., Scheeres Daniel
Conference: The 50th Lunar and Planetary Science Conference (The Woodlands, US, 20190318)
Ref HAL: hal02080373_v1
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Résumé: By means of extensive threedimensional contact dynamics simulations, we analyse the strength properties and microstructure of a granular asteroid, modelled as a selfgravitating cohesive granular aggregate composed of spherical particles, and subjected to diametrical compression tests. We show that, for a broad range of system parameters (shear rate, cohesive forces, asteroid diameter), the behaviour can be described by a modified inertial number that incorporates interparticle cohesion and gravitational forces.




Rheology and structure of polydisperse threedimensional packings of spheres
Auteur(s): Cantor D., Azema E., Sornay Philippe, Radjai F.
(Article) Publié:
Physical Review E, vol. 98 p.052910 (2018)
Ref HAL: hal01943671_v1
DOI: 10.1103/PhysRevE.98.052910
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Résumé: We use threedimensional contact dynamics simulations to analyze the rheology of polydisperse packings of spherical particles subjected to simple shear. The macroscopic and microstructural properties of several packings are analyzed as a function of their size span (from nearly monodisperse to highly polydisperse). Consistently with previous twodimensional simulations, we find that the shear strength is independent of the size span despite the increase of packing fraction with size polydispersity. At the grain scale, we analyze the particle connectivity, force transmission, and the corresponding anisotropies of the contact and force networks. We show that force distributions become increasingly broader as the size span increases. In particular, stronger forces are captured by large particles, which are also better connected creating the socalled granular backbone. Throughout this backbone friction mobilization is rare and compressive forces control the stability of such structure. In return, small particles create an important population of rattlers discarded of the strength and granular structure analysis. As a consequence, the contact anisotropy declines with size span, whereas the force and branch anisotropies increase. These microstructural compensations allow us to explain the independence of the shear strength from particle size polydispersity.




Scaling behavior of cohesive selfgravitating aggregates
Auteur(s): Azema E., Sánchez Paul, Scheeres Daniel
(Article) Publié:
Physical Review E, vol. 98 p. (2018)
Ref HAL: hal01873746_v1
DOI: 10.1103/PhysRevE.98.030901
Exporter : BibTex  endNote
Résumé: By means of extensive threedimensional contact dynamics simulations, we analyze the strength properties and microstructure of a granular asteroid, modeled as a selfgravitating cohesive granular aggregate composed of spherical particles, and subjected to diametrical compression tests. We show that, for a broad range of system parameters (shear rate, cohesive forces, asteroid diameter), the behavior can be described by a modified inertial number that incorporates interparticle cohesion and gravitational forces. At low inertial numbers, the behavior is ductile with a welldefined stress peak that scales with internal pressure with a prefactor 0.9. As the inertial number increases, both the prefactor and fluctuations around the mean increase, evidencing a dynamical crisis resulting from the destabilizing effect of particle inertia. From a micromechanical description of the contact and force networks, we propose a model that accounts for solid fraction, local stress, particle connectivity, and granular texture. In the limit of small inertial numbers, we find a very good agreement of the theoretical estimate of compressive strength, evidencing the major role of these structural parameters for the modeled aggregates.




Rheology of granular materials composed of crushable particles
Auteur(s): Nguyen D. H., Azema E., Sornay Philippe, Radjai F.
(Article) Publié:
European Physical Journal E, vol. 41 p.50 (2018)
Ref HAL: hal01767859_v1
DOI: 10.1140/epje/i2018116561
Exporter : BibTex  endNote
Résumé: We investigate sheared granular materials composed of crushable particles by means of contact dynamics simulations and the bondedcell model for particle breakage. Each particle is paved by irregular cells interacting via cohesive forces. In each simulation, the ratio of the internal cohesion of particles to the confining pressure, the relative cohesion, is kept constant and the packing is subjected to biaxial shearing. The particles can break into two or more fragments when the internal cohesive forces are overcome by the action of compressive force chains between particles. The particle size distribution evolves during shear as the particles continue to break. We find that the breakage process is highly inhomogeneous both in the fragment sizes and their locations inside the packing. In particular, a number of large particles never break whereas a large number of particles are fully shattered. As a result, the packing keeps the memory of its initial particle size distribution, whereas a powerlaw distribution is observed for particles of intermediate size due to consecutive fragmentation events whereby the memory of the initial state is lost. Due to growing polydispersity, dense shear bands are formed inside the packings and the usual dilatant behavior is reduced or cancelled. Hence, the stressstrain curve no longer passes through a peak stress, and a progressive monotonic evolution towards a pseudosteady state is observed instead. We find that the crushing rate is controlled by the confining pressure. We also show that the shear strength of the packing is well expressed in terms of contact anisotropies and force anisotropies. The force anisotropy increases while the contact orientation anisotropy declines for increasing internal cohesion of the particles. These two effects compensate each other so that the shear strength is nearly independent of the internal cohesion of particles.




Inertial shear flow of assemblies of frictionless polygons: Rheology and microstructure
Auteur(s): Azema E., Radjai F., Roux JeanNoël
(Article) Publié:
European Physical Journal E, vol. 41 p. (2018)
Ref HAL: hal01675180_v1
DOI: 10.1140/epje/i2018116089
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1 citation
Résumé: Motivated by the understanding of shape effects in granular materials, we numerically investigate the macroscopic and microstructural properties of anisotropic dense assemblies of frictionless polydisperse rigid pentagons in shear flow, and compare them with similar systems of disks. Once subjected to large cumulative shear strains their rheology and microstructure are investigated in uniform steady states, depending on inertial number I, which ranges from the quasistatic limit (I ∼ 10 −5) to 0.2. In the quasistatic limit both systems are devoid of Reynolds dilatancy, i.e., flow at their random close packing density. Both macroscopic friction angle ϕ, an increasing function of I, and solid fraction ν, a decreasing function of I, are larger with pentagons than with disks at small I, but the differences decline for larger I and, remarkably , nearly vanish for I ∼ 0.2. Under growing I, the depletion of contact networks is considerably slower with pentagons, in which increasingly anisotropic, but still wellconnected forcetransmitting structures are maintained throughout the studied range. Whereas contact anisotropy and force anisotropy contribute nearly equally to the shear strength in disk assemblies, the latter effect dominates with pentagons at small I, while the former takes over for I of the order of 10 −2. The size of clusters of grains in sidetoside contact, typically comprising more than 10 pentagons in the quasistatic limit, very gradually decreases for growing I.


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