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/Matière Condensée/Matière Molle
 Physique/Mécanique
 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
 Physique/Matière Condensée

Dernieres productions scientifiques :


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
Exporter : BibTex  endNote
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.




Cohesive strength of iron ore granules
Auteur(s): Contreras Rafael Jaimes, Berger Nicolas, Izard Edouard, Douce JeanFrançois, Koltsov Alexey, Delenne J.Y., Azema E., Nezamabadi S., van Loo Frédéric, Pellenq Roland, Radjai F.
Conference: International Conference on Micromechanics of Granular Media (Powders & Grains) (Montpellier, FR, 20170703)
Actes de conférence: , vol. 140 p. (2017)
Ref HAL: hal01594572_v1
DOI: 10.1051/epjconf/201714008020
Exporter : BibTex  endNote
Résumé: We present an experimental and numerical investigation of the mechanical strength of crude iron ore (Hematite) granules in which capillary bonds between primary particles are the source of internal cohesion. The strength is measured by subjecting the granules to vertical compression between two plates. We show that the behavior of the granules is ductile with a welldefined plastic threshold which increases with the amount of water. It is found that the compressive strength scales with capillary cohesion with a prefactor that is nearly independent of size polydispersity for the investigated range of parameters but increases with friction coefficient between primary particles. This weak dependence may be attributed to the class of fine particles which, due to their large number, behaves as a cohesive matrix that controls the strength of the granule.




Shear strength and microstructure of polydisperse packings: The effect of size span and shape of particle size distribution
Auteur(s): Azema E., Linero Sandra, Estrada Nicolas, Lizcano Arcesio
(Article) Publié:
Physical Review E, vol. 96 p.022902 (2017)
Ref HAL: hal01576976_v1
DOI: 10.1103/PhysRevE.96.022902
Exporter : BibTex  endNote
3 citations
Résumé: By means of extensive contact dynamics simulations, we analyzed the effect of particle size distribution (PSD) on the strength and microstructure of sheared granular materials composed of frictional disks. The PSDs are built by means of a normalized β function, which allows the systematic investigation of the effects of both, the size span (from almost monodisperse to highly polydisperse) and the shape of the PSD (from linear to pronouncedly curved). We show that the shear strength is independent of the size span, which substantiates previous results obtained for uniform distributions by packing fraction. Notably, the shear strength is also independent of the shape of the PSD, as shown previously for systems composed of frictionless disks. In contrast, the packing fraction increases with the size span, but decreases with more pronounced PSD curvature. At the microscale, we analyzed the connectivity and anisotropies of the contacts and forces networks. We show that the invariance of the shear strength with the PSD is due to a compensation mechanism which involves both geometrical sources of anisotropy. In particular, contact orientation anisotropy decreases with the size span and increases with PSD curvature, while the branch length anisotropy behaves inversely.


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