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(61) Production(s) de RENOUF M.


LMGC90: a Contact Dynamics open source code for the simulation of granular asteroid with realistic regolith shapes. Application to the accretion process
Auteur(s): Sánchez Paul, Renouf M., Azema E., Mozul R.
Conference: Powders & Grains (Buenos Aires, AR, 20210705)
Actes de conférence: , vol. 249 p.14007 (2021)
Ref HAL: hal03259852_v1
DOI: 10.1051/epjconf/202124914007
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Résumé: Granular asteroids are naturally occurring gravitational aggregates (rubble piles) bound together by gravitational forces. For this reason, it is reasonable to use the theoretical concepts and numerical tools developed for granular media to study them. In this paper, we extend the field of applicability of the Contact Dynamic (CD) method, a class of non smooth discrete element approach, for the simulation of three dimensional granular asteroids. The CD method is particularly relevant to address the study of dense granular assemblies of a large number of particles of complex shape and broad particles size distribution, since it does not introduces numerical artefacts due to contact stiffness. We describe how the open source software LMGC90, interfaced with an external library for the calculation of selfgravity, is used to model the accretion process of spherical and irregular polyhedral particles.




A micromechanical compaction model for granular mix of soft and rigid particles
Auteur(s): CárdenasBarrantes Manuel, Cantor D., Barés J., Renouf M., Azema E.
Conference: Powders & Grains (Buenos Aires, AR, 20210705)
Actes de conférence: , vol. 249 p.02008 (2021)
Ref HAL: hal03259845_v1
DOI: 10.1051/epjconf/202124902008
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Résumé: We use bidimensional nonsmooth contact dynamics simulations to analyze the isotropic compaction of mixtures composed of rigid and deformable incompressible particles. Deformable particles are modeled using the finiteelement method and following a hyperelastic neoHookean constitutive law. The evolution of the packing fraction, bulk modulus and particle connectivity, beyond the jamming point, are characterized as a function of the applied stresses for different proportion of rigid/soft particles and two values of friction coefficient. Based on the granular stress tensor, a micromechanical expression for the evolution of the packing fraction and the bulk modulus are proposed. This expression is based on the evolution of the particle connectivity together with the bulk behaviour of a single representative deformable particle. A constitutive compaction equation is then introduced, set by welldefined physical quantities, given a direct prediction of the maximum packing fraction φ max as a function of the proportion of rigid/soft particles.




Highly strained mixtures of bidimensional soft and rigid grains: an experimental approach from the local scale
Auteur(s): Barés J., CárdenasBarrantes Manuel, Cantor D., Azema E., Renouf M.
Conference: Powders & Grains (Buenos Aires (virtual), AR, 20210705)
Actes de conférence: , vol. 249 p.05004 (2021)
Ref HAL: hal03259819_v1
DOI: 10.1051/epjconf/202124905004
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Résumé: Granular systems are not always homogeneous and can be composed of grains with very diﬀerent mechanical properties. To improve our understanding of the behavior of real granular systems, in this experimental study, we compress 2D bidisperse systems made of both soft and rigid grains. By means of a recently developed experimental setup, from the measurement of the displacementfield we can follow all the mechanical observables of this granular medium from the inside of each particle upto the whole system scale. We are able to detect the jamming transition from these observables and study their evolution deep in the jammed state for packing fractions as high as 0.915. We show the uniqueness of the behavior of such a system, in which way it is similar to purely soft or rigid systems and how it is diﬀerent from them. This study constitutes thefirst step toward a better understanding of mechanical behavior of granular materials that are polydisperse in terms of grain rheology.




Bulk modulus of soft particle assemblies under compression
Auteur(s): Cantor D., CárdenasBarrantes Manuel, Preechawuttipong Itthichai, Renouf M., Azema E.
Conference: Powders & Grains (Buenos Aires (virtual), AR, 20210705)
Actes de conférence: Powders & Grains 2021 – 9th International Conference on Micromechanics on Granular Media, vol. p. ()
Ref HAL: hal03259722_v1
DOI: 10.1051/epjconf/202124914014
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Résumé: Using a numerical approach based on the coupling of the discrete and finite element methods, we explore the variation of the bulk modulus K of soft particle assemblies undergoing isotropic compression. As the assemblies densify under pressurecontrolled boundary conditions, we show that the nonlinearities of K rapidly deviate from predictions standing on a smallstrain framework or the, socalled, Equivalent Medium Theory (EMT). Using the granular stress tensor and extracting the bulk properties of single representative grains under compression, we propose a model to predict the evolution of K as a function of the sample's solid fraction and a reference state as the applied pressure P ! 0. The model closely reproduces the trends observed in our numerical experiments confirming the behavior scalability of soft particle assemblies from the individual particle scale. Finally, we present the e↵ect of the interparticle friction on K's evolution and how our model easily adapts to such a mechanical constraint.




Shape or friction? Which of these characteristics drives the shear strength in granular systems?
Auteur(s): Binaree Theechalit, Azema E., Estrada Nicolas, Renouf M., Preechawuttipong Itthichai
Conference: Powders & Grains (Buenos Aires (virtual), AR, 20210705)
Actes de conférence: Powders & Grains 2021 – 9th International Conference on Micromechanics on Granular Media, vol. 249 p. (2021)
Ref HAL: hal03259703_v1
DOI: 10.1051/epjconf/202124906008
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Résumé: The shape of the particles and local friction, separately, are known to strongly affect the macroscopic properties of an assembly of grains. But the combined effects of these two parameters still remain poorly described. By means of extensive two dimensional contact dynamics simulations, we perform a systematic analysis of the interplay between friction and shape on strength properties of granular systems. The shape of the particles is varied from disks to triangles, while the friction is varied from 0 to 0.7. We find that the macroscopic friction first increases with angularity, but it may decline (for low friction values), saturate (for intermediates friction values), or continue to increase (for large friction values) for the most angular shapes. In other words, the effect of the particle's angularity on the shear strength depends on the level of sliding friction. In contrast, the effect of local friction on the shear strength does not depend on the specific properties of shape. The results presented here highlight the subtle coupling existing between shape and friction effects.




Micromechanical description of the compaction of soft pentagon assemblies
Auteur(s): CárdenasBarrantes Manuel, Cantor D., Barés J., Renouf M., Azema E.
(Article) Publié:
Physical Review E, vol. 103 p. (2021)
Ref HAL: hal03259685_v1
DOI: 10.1103/PhysRevE.103.062902
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Résumé: We analyze the isotropic compaction of assemblies composed of soft pentagons interacting through classical Coulomb friction via numerical simulations. The effect of the initial particle shape is discussed by comparing packings of pentagons with packings of soft circular particles. We characterize the evolution of the packing fraction, the elastic modulus, and the microstructure (particle rearrangement, connectivity, contact force, and particle stress distributions) as a function of the applied stresses. Both systems behave similarly: the packing fraction increases and tends asymptotically to a maximum value φ max , where the bulk modulus diverges. At the microscopic scale we show that particle rearrangements occur even beyond the jammed state, the mean coordination increases as a square root of the packing fraction, and the force and stress distributions become more homogeneous as the packing fraction increases. Soft pentagons experience larger particle rearrangements than circular particles, and such behavior decreases proportionally to the friction. Interestingly, the friction between particles also contributes to a better homogenization of the contact force network in both systems. From the expression of the granular stress tensor we develop a model that describes the compaction behavior as a function of the applied pressure, the Young modulus, and the initial shape of the particles. This model, settled on the joint evolution of the particle connectivity and the contact stress, provides outstanding predictions from the jamming point up to very high densities.




A damage criterion based on energy balance for isotropic cohesive zone model
Auteur(s): Chrysochoos A., Daridon L., Renouf M.
(Document sans référence bibliographique)
Résumé: The objective of this paper is to present an energy damage criterion for cohesive zone models (CZM) within the framework of the nonlinear thermodynamics of irreversible processes (TIP). An isotropic elastic damageable material is considered for isothermal transformations. Damage is then the only irreversible effect accompanying the deformation process and this mechanism is supposed to be fully dissipative. Once a separation law and a damage state variable have been chosen, the paper shows that the damage criterion can be automatically derived from the energy balance. From this observation, a CZM is derived for a given choice of tractionseparation law and damage state variable and the quality of its numerical predictions is analyzed using an experimental benchmark bending test extracted from literature. Finally, damage, elastic and dissipated energy fields around the crack path are shown during this rupture test.

