24 results on '"Nicot, François"'
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2. A novel multi-scale large deformation approach for modelling of granular collapse
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Xiong, Hao, Yin, Zhen-Yu, Nicot, François, Wautier, Antoine, Marie, Miot, Darve, Félix, Veylon, Guillaume, and Philippe, Pierre
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- 2021
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Catalog
3. Discrete Numerical Analysis of Failure Modes in Granular Materials
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Sibille, Luc, Prunier, Florent, Nicot, François, Darve, Félix, Oñate, Eugenio, editor, and Owen, Roger, editor
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- 2011
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4. Micromechanical analysis of second order work in granular media
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Hadda, Nejib, Nicot, François, Bourrier, Franck, Sibille, Luc, Radjai, Farhang, and Darve, Félix
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- 2013
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5. Physical processes within a 2D granular layer during an impact
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Bourrier, Franck, Nicot, François, and Darve, Félix
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- 2008
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6. On the Elastic and Plastic Strain Decomposition in Granular Materials
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Nicot, François and Darve, Félix
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- 2006
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7. Mesoscale Investigation of Fine Grain Contribution to Contact Stress in Granular Materials.
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Ma, Qirui, Wautier, Antoine, and Nicot, François
- Subjects
DISCRETE element method ,GRAIN size ,MECHANICAL behavior of materials ,IMPACT (Mechanics) ,GRANULAR materials - Abstract
Fine grains play an important role in mechanical properties of granular materials as they control how plastic strain may develop, which has a noticeable impact on mechanical stability. In this work, we use numerical simulations based on a discrete element method (DEM) to analyze the stress contribution of fine grains to the total stress. Different from usual DEM simulations, the analysis is conducted directly at the mesoscopic scale by considering an idealized grain assembly. The results show how fine grains get progressively jammed and increasingly participate in stress transmission. Fine contribution to contact stress is shown to be nonisotropic. The principal anisotropy direction coincides with the principal direction of contraction and the anisotropy ratio (i.e., the ratio between the largest and the smallest eigenvalues of the fine stress) is shown to be limited (σmax/σmin≃2). By performing strain controlled directional analyses, an analytical model is proposed to account for the stress contribution of fine grains along various loading paths. Its simple form will help to enrich advanced micromechanically-based constitutive formulations and better account for the constitutive behavior of widely graded granular materials. [ABSTRACT FROM AUTHOR] more...
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- 2022
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8. Flow impact on granular force chains and induced instability
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Wautier, A., Bonelli, Stéphane, Nicot, François, Risques, Ecosystèmes, Vulnérabilité, Environnement, Résilience (RECOVER), Aix Marseille Université (AMU)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Erosion torrentielle neige et avalanches (UR ETGR (ETNA)), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), and Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Aix Marseille Université (AMU) more...
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Physics::Fluid Dynamics ,INSTABILITIES ,GRANULAR MATERIAL ,[SDE]Environmental Sciences ,INTERNAL FLOW ,FORCE CHAINS ,FLUID FORCE FLUCTUATIONS - Abstract
[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; With today's fully coupled DEM/PFV simulations, the impact of an internal fluid flow on the mechanical stability of a granular material is assessed at the scale of a three-dimensional representative elementary volume. To isolate the specific impact of the fluid on the contact network, a granular sample in which rattlers have been initially removed is considered while a fluid pressure drop is applied under constant mechanical loading. Although the initial state is reputed to be unstable according to the second order work criterion, it is shown that i) an internal fluid flow is able to trigger the underlying instability on its own and ii) the flow direction has no influence because of local fluid force fluctuations. In addition, the microscale mechanisms occurring during the sample collapse are investigated and it is shown that the fluid perturbation induces a decrease in kinematic constraints around force chains, which is characteristic of a local loss of stability. more...
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- 2018
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9. Micro-inertia origin of instabilities in granular materials
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Wautier, Antoine, Bonelli, Stéphane, Nicot, François, Erosion torrentielle neige et avalanches (UR ETGR (ETNA)), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Risques, Ecosystèmes, Vulnérabilité, Environnement, Résilience (RECOVER), Aix Marseille Université (AMU)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), AgroParisTech, Ouvrages hydrauliques et hydrologie (UR OHAX), and Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Aix Marseille Université (AMU) more...
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[PHYS.MECA.MEMA]Physics [physics]/Mechanics [physics]/Mechanics of materials [physics.class-ph] ,Unjamming ,Bending ,Stability and bifurcation ,[PHYS.MECA.SOLID]Physics [physics]/Mechanics [physics]/Solid mechanics [physics.class-ph] ,[SPI.GCIV.GEOTECH]Engineering Sciences [physics]/Civil Engineering/Géotechnique ,Force chain ,Second order work ,[PHYS.MECA.SOLID]Physics [physics]/Mechanics [physics]/Mechanics of the solides [physics.class-ph] ,Granular material - Abstract
[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; Within the framework of the second order work theory, the onset of instabilities is explored numerically in loose granular materials through three dimensional DEM simulations. Stress controlled directional analysis are performed in Rendulic's plane and a particular attention is paid to transient evolutions at the microscale. Thanks to a micromechanical analysis, the onset and development of transient mechanical instabilities is explored. It is shown that these instabilities result from the unjamming and bending of a few force chains associated with a local burst of kinetic energy. This burst of kinetic energy propagates to the whole sample and provokes a generalized unjamming of force chains. As force chains buckle, a phase transition from a quasi-static to an inertial regime is observed. At the macroscopic scale, this results in a transient softening and a loss of controllability. After the collapse of existing force chains, the development of plastic strain is eventually stopped as new stable force chains are built. more...
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- 2018
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10. Micromechanical modelling of suffusion: towards the stability analysis of hydraulic structures
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Wautier, A., Nicot, François, Bonelli, Stéphane, Risques, Ecosystèmes, Vulnérabilité, Environnement, Résilience (RECOVER), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Aix Marseille Université (AMU), Erosion torrentielle neige et avalanches (UR ETGR (ETNA)), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Euripides Papamichos, Panos Papanastasiou, Elena Pasternak, Arcady Dyskin, and Aix Marseille Université (AMU)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA) more...
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ESSAI TRIAXIAL ,granular material ,suffusion ,[SDE.IE]Environmental Sciences/Environmental Engineering ,internal erosion ,EROSION INTERNE ,[SDE]Environmental Sciences ,METHODE DES ELEMENTS DISCRETS ,MATERIAU GRANULAIRE ,discret element method - Abstract
[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; Suffusion is the most controversial of the process of internal erosion and piping as there is a lack of microscopic understanding of the degradation processes at stake in saturated soils subjected to an internal flow. Thanks to the use of a DEM-PFV (Discrete Element Method - Pore-scale Finite Volume) approach, this study addresses the fully coupled problem of the suffusion of a non cohesive granular material. Eligible particles to grain detachment and grain transport are characterized from a micromechanical point of view thanks to the use of an enhanced force chain definition and the definition of a pore network. A Representative Elementary Volume with respect to the grain detachment and grain transport is then quantified. more...
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- 2017
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11. DEM investigations of internal erosion: Grain transport in the light of micromechanics.
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Wautier, Antoine, Bonelli, Stéphane, and Nicot, François
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MICROSTRUCTURE ,GRANULAR materials ,GRAIN transportation ,DISCRETE element method ,COUPLINGS (Gearing) - Abstract
Summary: Internal erosion by suffusion can change dramatically the constitutive behavior of granular materials by modifying the fabric of granular materials. In this study, the effect of an internal fluid flow on granular materials is investigated at the material point scale using the numerical coupling between a discrete element method (DEM) and a pore‐scale finite volume (PFV) coupling scheme. The influence of the stress state and the hydraulic loading (direction and intensity) on the occurrence of grain transport in dense widely graded granular samples is thus investigated and interpreted in terms of micromechanics. In particular, it is shown that grain transport is increased when the macroscopic flow direction is aligned with the privileged force chain orientation. The stress‐induced microstructure modifications are shown to influence the transport distances by controlling the number of rattlers. [ABSTRACT FROM AUTHOR] more...
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- 2019
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12. The role of force chains in granular materials: from statics to dynamics.
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Zhang, Lingran, Nguyen, Nho Gia Hien, Lambert, Stéphane, Nicot, François, Prunier, Florent, and Djeran-Maigre, Irini
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GRANULAR materials ,AXIAL loads ,IMPACT (Mechanics) ,MICROSTRUCTURE ,MECHANICAL buckling - Abstract
This paper investigates the role of force chains in granular materials under both quasistatic biaxial loading and dynamic impact loading conditions. This study is mainly interested in investigating the role of force chains on the global mechanical responses of samples as well as on the microstructure of granular materials. For this purpose, discrete element methods are adopted to perform different loading tests. Granular materials are modelled as aggregations of poly-disperse spherical particles. Results first show that force chains are responsible for the strength of the sample: in 2D biaxial test, the establishment and buckling of force chains are responsible for the evolution in terms of deviatoric stress; in 3D dynamic impact test, the development and the buckling of force chains are responsible for the evolution of impact force on the impacting projectile. Second, force chains are found to play an important role in themicrostructure of granular materials: in statics, the buckling of force chains mainly locates inside the shear band, and is related to the increase in local void around the buckling grain as well as the increase in kinetic energy inside the sample; in dynamic test, the number of buckled force chains is correlated with the energy dissipation inside the sample. [ABSTRACT FROM AUTHOR] more...
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- 2017
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13. The H-microdirectional model: Accounting for a mesoscopic scale
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Nicot, François and Darve, Félix
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NUMERICAL solutions to boundary value problems , *MICROMECHANICS , *MESOSCOPIC phenomena (Physics) , *PHENOMENOLOGICAL theory (Physics) , *COMPOSITE materials , *MATHEMATICAL models - Abstract
Abstract: Solving boundary value problems requires implementation of sufficiently robust constitutive models. Most models try to incorporate a great deal of phenomenological ingredients, but this refining often leads to overcomplicated formulations, requiring a large number of parameters to be identified. A powerful alternative can be found with micromechanical models, where the medium is described as a distribution of elementary sets of grains. The complexity is not related to the constitutive description, but to the multiplicity of contacts oriented along all the directions of the physical space. This paper proposes an advanced micromechanical model that introduces an intermediate scale (mesoscopic scale): elementary hexagonal patterns of adjoining particles. This is advantageous with respect to current micromechanical models that generally describe the material through a single distribution of contacts. This new approach makes it possible to take many constitutive properties into account in a very natural way, such as the occurrence of diffuse failure modes. These preliminary results are presented in order to give clear insights into the capability of such multiscale approaches. [Copyright &y& Elsevier] more...
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- 2011
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14. Micromechanical Formulation of Stress Dilatancy as a Flow Rule in Plasticity of Granular Materials.
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Wan, Richard, Nicot, François, and Darve, Félix
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MICROMECHANICS , *MICROELECTROMECHANICAL systems , *MATERIAL plasticity , *GRANULAR materials - Abstract
The paper presents micromechanical formulations of stress dilatancy and their connection to a flow rule in classical elastoplasticity. Dilatancy is inarguably the manifestation of an internal kinematic constraint involving both particle shape and connectivity (texture or fabric) with operative interparticle friction against applied stresses. However, this notion of microstructural dependence is nonexistent in most stress-dilatancy formulations in the literature. We present two different micromechanical approaches that arrive at stress-dilatancy expressions with embedded micromechanical information in the form of a second-order fabric tensor. In connection to stress dilatancy, the underlying nature of the flow rule is next discussed with respect to the dependence of the plastic strain increment vector on the direction of loading (stress increment). It is demonstrated analytically that the flow rule is singular in three-dimensional stress and strain conditions. Finally, the dependencies of dilatancy on fabric are illustrated through various numerical simulations using the micromechanically enriched stress-dilatancy models and a discrete element method. [ABSTRACT FROM AUTHOR] more...
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- 2010
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15. Micro-mechanical bases of some salient constitutive features of granular materials
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Nicot, François and Darve, Félix
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GRANULAR materials , *ANISOTROPY , *ASYMPTOTIC homogenization , *PARTIAL differential equations - Abstract
Abstract: Although phenomenological constitutive models have the ability to exhibit most salient macroscopic features of granular materials, they generally do not provide any convincing interpretation of them: their basic origin remains hidden. It is now well established that the micro-structure of granular materials plays a significant role in their overall constitutive behavior. In the past few years, a great deal of theoretical and experimental research has been devoted to this domain, giving rise to efficient micro-mechanical approaches. First, this paper reviews the micro-directional model, which is a micro-mechanically based constitutive relation. Then an extension is proposed to describe the possible collapse of force chains. This micro-structural adjunction is shown to be sufficient to simulate work-hardening and softening mechanisms. A granular assembly, containing a multitude of frictional contacts whose orientation is generally anisotropically distributed, exhibits various other typical features such as the nonassociated character of plastic strains. The micro-structural origin of this feature is investigated, and further conclusions related to the existence of a regular or a singular flow rule are drawn. [Copyright &y& Elsevier] more...
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- 2007
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16. Basic features of plastic strains: From micro-mechanics to incrementally nonlinear models
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Nicot, François and Darve, Félix
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STRAINS & stresses (Mechanics) , *NONLINEAR statistical models , *ELASTOPLASTICITY , *GRANULAR materials - Abstract
Abstract: Most rate-independent constitutive relations for granular materials are based on the existence of a regular flow rule. This assumption states that once the mechanical state of a material point belongs to the yield surface, then the direction of the plastic strains is independent of the loading direction. In this paper, the notion of a regular flow rule is shown to exist only for two-dimensional and axisymmetric loading conditions. By considering our incrementally nonlinear constitutive model, it is established that this notion disappears as soon as more general loading conditions are applied, as also predicted from discrete element simulations. Moreover, a sound micro-mechanical interpretation of the vanishing of a regular flow rule in three-dimensional loading conditions is given from a multi-scale perspective using the micro-directional model. This model highlights the great influence of the loading history on the shape of the plastic Gudehus response-envelope. [Copyright &y& Elsevier] more...
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- 2007
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17. From microscopic to macroscopic second-order work in granular assemblies
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Nicot, François, Sibille, Luc, Donze, Frédéric, and Darve, Félix
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GRANULAR materials , *SOLID state physics , *COMPACTING , *BULK solids - Abstract
Abstract: It is now well established that for non-associated materials such as geomaterials, a broad domain exists, strictly within the plastic limit, where different failure modes can coexist. In particular, material instability as defined by Hill [Hill, R., 1958. A general theory of uniqueness and stability in elastic–plastic solids. J. Mech. Phys. Solids, 6, 236–249], related to the vanishing of the second-order work, can potentially occur. In this paper, we focus on granular materials and establish from theoretical considerations that the macroscopic second-order work on the assembly scale is related to the microscopic second-order work computed on each contact. This question is examined from a multi-scale approach, and the relation between macroscopic and microscopic second-order works is brought to light using a micro-mechanically based model. Finally, these theoretical results are confirmed from numerical simulations based on a discrete element method. [Copyright &y& Elsevier] more...
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- 2007
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18. Micro-mechanical investigation of material instability in granular assemblies
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Nicot, François and Darve, Félix
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GRANULAR materials , *ASYMPTOTIC homogenization , *PARTICLES , *STABILITY (Mechanics) - Abstract
Abstract: It is now well established that for non-associated materials such as geomaterials, there exists a wide domain strictly within the plastic limit where different failure modes can coexist. In particular, material instability in the sense given by Hill, related to the vanishing of the second-order work, can potentially occur. In this paper we examine the occurrence of such instabilities from the simulation of drained triaxial paths, followed by the computation of two-dimensional, then fully three-dimensional Gudehus response-envelopes using the micro-directional model. This model can be seen in the continuity of Hill’s multi-slip theory, because it accounts for the association of a large number of elementary elasto-plastic bodies. Each body is linked to a contact direction in physical space and therefore takes into account the behavior of the contacts oriented along that direction. Simulations confirmed that some loading directions led to the vanishing of the second-order work. In line with the research initiated by Mandel, a micro-mechanical analysis of the origin of these potential instabilities revealed that this macro-scale phenomenon could be directly related to the constitutive nature of the local contact model between neighboring particles. Finally, this investigation provides a clear physical understanding of Hill’s material stability condition for frictional materials. [Copyright &y& Elsevier] more...
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- 2006
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19. Rattlers' contribution to granular plasticity and mechanical stability.
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Wautier, Antoine, Bonelli, Stéphane, and Nicot, François
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MATERIAL plasticity , *MICROSTRUCTURE , *STRAINS & stresses (Mechanics) , *CYCLIC loads , *GRANULAR materials - Abstract
Abstract The mechanical behavior of granular materials is widely governed by microstructure reorganizations. This constant evolution of the microscale geometry is often taken into account directly at the macroscale within the plasticity context, and more particularly non-associated plasticity. In this paper we propose to revisit the non-associated plastic behavior of granular materials with respect to material instability assessment in terms of the loss of positiveness of the second-order work. It is shown that large incremental plastic strain is a necessary condition for the existence of mechanical instability. The ability of a material to develop substantial plastic incremental strain is then related to the existence of rattlers, i.e., free particles that get jammed into force chains when existing contact networks fail to adapt to incremental loadings. This link between rattlers, plastic deformation and the vanishing of the second-order work is explicitly derived i) from the micro-formulation of the second-order work and ii) directly from discrete element simulations. Highlights • Material mechanical stability is investigated from a micromechanics perspective. • The stabilizing role played by free particles is highlighted. • The influence of rattlers on the intensity of plastic strain increments is shown. • The link between fabric anisotropy and the non-associate flow rule direction is derived. [ABSTRACT FROM AUTHOR] more...
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- 2019
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20. Discrete dynamic modelling of the mechanical behaviour of a granular soil.
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Zhang, Lingran, Lambert, Stéphane, and Nicot, François
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SOIL granularity , *DYNAMIC models , *KINETIC energy , *ELASTOPLASTICITY , *DISCRETE element method , *ROCK mechanics - Abstract
This paper investigates the interaction between a falling rock boulder and a granular medium through numerical modelling based on a discrete element method. The boulder is modelled as a single sphere with an incident velocity, and the medium is modelled as an assembly composed of poly-disperse spherical particles. A classical elastic-plastic contact law is implemented with rolling resistance to consider the particle shape effects. The numerical modelling is validated by comparison with results from the literature in terms of impact force, impact duration and the boulder’s penetration depth of the boulder. Then the model is used to investigate the energy propagation within the impacted medium as well as the boulder bouncing. The energy propagation processes are investigated by analysing the space distribution of kinetic energy, elastic strain energy and energy dissipation within the medium over time. The boulder bouncing occurrence is studied, varying the impact conditions in terms of medium thickness and boulder size. Relations between the bouncing of the boulder and the response of the granular medium are finally discussed. [ABSTRACT FROM AUTHOR] more...
- Published
- 2017
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21. 3D DEM simulations of cyclic loading-induced densification and critical state convergence in granular soils.
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Wang, Tao, Wautier, Antoine, Tang, Chao-Sheng, and Nicot, François
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CYCLIC loads , *DISCRETE element method , *SOIL granularity , *MATERIAL plasticity , *GRANULAR materials - Abstract
Granular soils exhibit very complex responses when subjected to cyclic loading. Understanding the cyclic behavior of such materials is not only crucial for engineering applications but also the bottleneck of most of constitutive models. This study employs 3D Discrete Element Method (DEM) simulations to explore the accumulative plastic deformation and the internal fabric evolution within granular soils during cyclic loading. Two novel observations are identified: (1) A distinct and unique linear relationship between post-cyclic loading void ratio e and log (p*/p 0) is found independent of the amplitude of cyclic load and the initial stress state prior to cyclic loading, where p* is the mean pressure incorporating cyclic loading stress and p 0 is the mean pressure prior to cyclic loading; (2) When resuming drained triaxial loadings after cyclic loadings, we observe that both microstructural and macroscopic variables converge to the same values they would have reached for pure monotonic drained triaxial loadings. This intriguing behavior underscores and extends to more general loading paths the influential and attractive power of the critical state. [ABSTRACT FROM AUTHOR] more...
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- 2024
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22. Onset of Immersed Granular Avalanches by DEM-LBM Approach
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Delenne, Jean-Yves, Mansouri, M., Radjaї, F., Youssoufi, M. S. El, Seridi, A., Bonelli, Stéphane, editor, Dascalu, Cristian, editor, and Nicot, François, editor
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- 2011
- Full Text
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23. Length Scales for Nonaffine Deformation in Localized, Granular Shear
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Rechenmacher, Amy L., Abedi, Sara, Bonelli, Stéphane, editor, Dascalu, Cristian, editor, and Nicot, François, editor
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- 2011
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24. Deciphering D’Alemberts Dream: New Tools for Uncovering Rules for Self-Organized Pattern Formation in Geomaterials
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Tordesillas, Antoinette, Walker, David M., Bonelli, Stéphane, editor, Dascalu, Cristian, editor, and Nicot, François, editor
- Published
- 2011
- Full Text
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