This paper presents a numerical technique to model soft particle materials in which the particles can undergo large deformations. It combines an implicit finite strain formalism of the Material Point Method and the Contact Dynamics method. In this framework, the large deformations of individual particles as well as their collective interactions are treated consistently. In order to reduce the computational cost, this method is parallelised using the Message Passing Interface (MPI) strategy. Using this approach, we investigate the uniaxial compaction of 2D packings composed of particles governed by a Neo-Hookean material behaviour. We consider compressibility rates ranging from fully compressible to incompressible particles. The packing deformation mechanism is a combination of both particle rearrangements and large deformations, and leads to high packing fractions beyond the jamming state. We show that the packing strength declines when the particle compressibility decreases, and the packing can deform considerably. We also discuss the evolution of the connectivity of the particles and particle deformation distributions in the packing. (C) 2018 Elsevier B.V. All rights reserved.

VL - 237 UR - https://linkinghub.elsevier.com/retrieve/pii/S0010465518303904 JO - Computer Physics Communications ER - TY - JOUR T1 - Mechanical strength of wet particle agglomerates JF - Mechanics Research Communications Y1 - 2018 A1 - Vo, Thanh-Trung A1 - Patrick Mutabaruka A1 - Saeid Nezamabadi A1 - Jean-Yves Delenne A1 - Izard, Edouard A1 - Roland Jean-Marc Pellenq A1 - Farhang Radjaï AB -Using particle dynamics simulations, we investigate the strength and microstructure of agglomerates of wet frictional particles subjected to axial compression. The numerical model accounts for the cohesive and viscous effects of the binding liquid up to a debonding distance with the liquid assumed to be distributed homogeneously inside the agglomerate. We show that wet agglomerates undergo plastic deformation due to the rearrangements of primary particles during compression. The compressive strength is thus characterized by the plastic threshold before the onset of failure by the irreversible loss of wet contacts between primary particles. We find that the agglomerate plastic threshold is proportional to the characteristic cohesive stress defined from the liquid-vapor surface tension and the mean diameter of primary particles, with a prefactor that is a nearly linear function of the debonding distance and increases with size span. We analyze the agglomerate microstructure and, considering only the cohesive capillary forces at all bonds between primary particles, we propose an expression of the plastic strength as a function of the texture parameters such as the wet coordination number and packing fraction. This expression is shown to be consistent with our simulations up to a multiplicative factor reflecting the distribution of the capillary bridges. (C) 2018 Published by Elsevier Ltd.

VL - 92 UR - https://www-sciencedirect-com.libproxy.mit.edu/science/article/pii/S0093641318301216 JO - Mechanics Research Communications ER - TY - JOUR T1 - Multiscale modeling for bioresources and bioproducts JF - Innovative Food Science & Emerging Technologies Y1 - 2018 A1 - Barnabe, M. A1 - Blanc, Nicolas A1 - Chabin, T. A1 - Jean-Yves Delenne A1 - Duri, A. A1 - Frank, Xavier A1 - Hugouvieux, V. A1 - Lutton, E. A1 - Mabille, F. A1 - Saeid Nezamabadi A1 - Perrot, N. A1 - Farhang Radjaï A1 - Ruiz, T. A1 - Tonda, A. AB -Designing and processing complex matter and materials are key objectives of bioresource and bioproduct research. Modeling approaches targeting such systems have to account for their two main sources of complexity: their intrinsic multi-scale nature; and the variability and heterogeneity inherent to all living systems. Here we provide insight into methods developed at the Food & Bioproduct Engineering division (CEPIA) of the French National Institute of Agricultural Research (INRA). This brief survey focuses on innovative research lines that tackle complexity by mobilizing different approaches with complementary objectives. On one hand cognitive approaches aim to uncover the basic mechanisms and laws underlying the emerging collective properties and macroscopic behavior of soft-matter and granular systems, using numerical and experimental methods borrowed from physics and mechanics. The corresponding case studies are dedicated to the structuring and phase behavior of biopolymers, powders and granular materials, and to the evolution of these structures caused by external constraints. On the other hand machine learning approaches can deal with process optimizations and outcome predictions by extracting useful information and correlations from huge datasets built from experiments at different length scales and in heterogeneous conditions. These predictive methods are illustrated in the context of cheese ripening, grape maturity prediction and bacterial production.

VL - 46 UR - https://linkinghub.elsevier.com/retrieve/pii/S1466856417302230 IS - Special Issue: SI JO - Innovative Food Science & Emerging Technologies ER - TY - JOUR T1 - Rheology of granular materials composed of crushable particles JF - The European Physical Journal E Y1 - 2018 A1 - Duc-Hanh Nguyen A1 - Emilien Azéma A1 - Philippe Sornay A1 - Farhang Radjaï KW - CONTACT DYNAMICS METHOD; DISCRETE ELEMENT METHOD; SHEAR BANDS; NUMERICAL-SIMULATION; BED COMMINUTION; FRAGMENTATION; BREAKAGE; ROCK; DEM; MODEL AB -We investigate sheared granular materials composed of crushable particles by means of contact dynamics simulations and the bonded-cell 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 power-law 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 stress-strain curve no longer passes through a peak stress, and a progressive monotonic evolution towards a pseudo-steady 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.

VL - 41 UR - http://link.springer.com/10.1140/epje/i2018-11656-1 IS - 4 JO - Eur. Phys. J. E ER - TY - JOUR T1 - Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods JF - Physical Review E Y1 - 2018 A1 - Jeff Ngoma A1 - Pierre Philippe A1 - Stéphane Bonelli A1 - Farhang Radjaï A1 - Jean-Yves Delenne AB -We present here a numerical study dedicated to the fluidization of a submerged granular medium induced by a localized fluid injection. To this end, a two-dimensional (2D) model is used, coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM) for a relevant description of fluid-grains interaction. An extensive investigation has been carried out to analyze the respective influences of the different parameters of our configuration, both geometrical (bed height, grain diameter, injection width) and physical (fluid viscosity, buoyancy). Compared to previous experimental works, the same qualitative features are recovered as regards the general phenomenology including transitory phase, stationary states, and hysteretic behavior. We also present quantitative findings about transient fluidization, for which several dimensionless quantities and scaling laws are proposed, and about the influence of the injection width, from localized to homogeneous fluidization. Finally, the impact of the present 2D geometry is discussed, by comparison to the real three-dimensional (3D) experiments, as well as the crucial role of the prevailing hydrodynamic regime within the expanding cavity, quantified through a cavity Reynolds number, that can presumably explain some substantial differences observed regarding upward expansion process of the fluidized zone when the fluid viscosity is changed.

VL - 97 UR - https://link.aps.org/doi/10.1103/PhysRevE.97.052902 IS - 5 JO - Phys. Rev. E ER - TY - JOUR T1 - Cohesive strength of iron ore granules JF - EPJ Web of Conferences Y1 - 2017 A1 - Contreras, Rafael Jaimes A1 - Berger, Nicolas A1 - Izard, Edouard A1 - Douce, Jean-François A1 - Koltsov, Alexey A1 - Jean-Yves Delenne A1 - Emilien Azéma A1 - Saeid Nezamabadi A1 - van Loo, Frédéric A1 - Roland Jean-Marc Pellenq A1 - Farhang Radjaï ED - Luding, S. AB -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 well-defined plastic threshold which increases with the amount of water. It is found that the compressive strength scales with capillary cohesion with a pre-factor 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.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714008020 IS - 10141146 JO - EPJ Web Conf. ER - TY - JOUR T1 - Compaction of granular materials composed of deformable particles JF - EPJ Web of Conferences Y1 - 2017 A1 - Thanh Hai Nguyen A1 - Saeid Nezamabadi A1 - Jean-Yves Delenne A1 - Farhang Radjaï ED - Luding, S. AB -In soft particle materials such as metallic powders the particles can undergo large deformations without rupture. The large elastic or plastic deformations of the particles are expected to strongly affect the mechanical properties of these materials compared to hard particle materials more often considered in research on granular materials. Herein, two numerical approaches are proposed for the simulation of soft granular systems: (i) an implicit formulation of the Material Point Method (MPM) combined with the Contact Dynamics (CD) method to deal with contact interactions, and (i) Bonded Particle Model (BPM), in which each deformable particle is modeled as an aggregate of rigid primary particles using the CD method. These two approaches allow us to simulate the compaction of an assembly of elastic or plastic particles. By analyzing the uniaxial compaction of 2D soft particle packings, we investigate the effects of particle shape change on the stress-strain relationship and volume change behavior as well as the evolution of the microstructure.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714005013 JO - EPJ Web Conf. ER - TY - JOUR T1 - Effect of particle size distribution on 3D packings of spherical particles JF - EPJ Web of Conferences Y1 - 2017 A1 - Taiebat, Mahdi A1 - Patrick Mutabaruka A1 - Roland Jean-Marc Pellenq A1 - Farhang Radjaï ED - Saeid Nezamabadi ED - Luding, S. ED - Jean-Yves Delenne AB -We use molecular dynamics simulations of frictionless spherical particles to investigate a class of polydisperse granular materials in which the particle size distribution is uniform in particle volumes. The particles are assembled in a box by uniaxial compaction under the action of a constant stress. Due to the absence of friction and the nature of size distribution, the generated packings have the highest packing fraction at a given size span, defined as the ratio *α* of the largest size to the smallest size. We find that, up to *α* = 5, the packing fraction is a nearly linear function of *α*. While the coordination number is nearly constant due to the isostatic nature of the packings, we show that the connectivity of the particles evolves with *α*. In particular, the proportion of particles with 4 contacts represents the largest proportion of particles mostly of small size. We argue that this particular class of particles occurs as a result of the high stability of local configurations in which a small particle is stuck by four larger particles.

We use molecular dynamics simulations to investigate the effects of root bending stiffness and packing fraction on the path followed by a growing root in 2D packings of grains representing a soil. The root is modeled as a chain of elements that can grow in length and change their direction depending on the forces exerted by soil grains. We show that the root shape is mainly controlled by the bending stiffness of its apex. At low stiffness, the root randomly explores the pore space whereas at sufficiently high stiffness, of the order of soil hardness multiplied by mean grain size, the root follows a straight path across the soil. Between these two limits, the root shape can be characterized by the standard deviation of its re-directions at the scale of soil grains. We find that this shape parameter varies as a power-law function of the normalized bending stiffness.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714014013 JO - EPJ Web Conf. ER - TY - JOUR T1 - Modeling soft granular materials JF - Granular Matter Y1 - 2017 A1 - Saeid Nezamabadi A1 - Thanh Hai Nguyen A1 - Jean-Yves Delenne A1 - Farhang Radjaï AB -Soft-grain materials such as clays and other colloidal pastes share the common feature of being composed of grains that can undergo large deformations without rupture. For the simulation of such materials, we present two alternative methods: (1) an implicit formulation of the material point method (MPM), in which each grain is discretized as a collection of material points, and (2) the bonded particle model (BPM), in which each soft grain is modeled as an aggregate of rigid particles using the contact dynamics method. In the MPM, a linear elastic behavior is used for the grains. In order to allow the aggregates in the BPM to deform without breaking, we use long-range center-to-center attraction forces between the primary particles belonging to each grain together with steric repulsion at their contact points. We show that these interactions lead to a plastic behavior of the grains. Using both methods, we analyze the uniaxial compaction of 2D soft granular packings. This process is nonlinear and involves both grain rearrangements and large deformations. High packing fractions beyond the jamming state are reached as a result of grain shape change for both methods. We discuss the stress-strain and volume change behavior as well as the evolution of the connectivity of the grains. Similar textures are observed at large deformations although the BPM requires higher stress than the MPM to reach the same level of packing fraction.

VL - 19 IS - 1 JO - Granular Matter ER - TY - Generic T1 - MPM with Frictional Contact for Application to Soft Particulate Materials T2 - PROCEEDINGS OF THE 1ST INTERNATIONAL CONFERENCE ON THE MATERIAL POINT METHOD (MPM 2017) Book Series: Procedia Engineering Y1 - 2017 A1 - Saeid Nezamabadi A1 - Thanh Hai Nguyen A1 - Jean-Yves Delenne A1 - Julien Averseng A1 - Frank, Xavier A1 - Farhang Radjaï ED - Rohe, A ED - Kenichi Soga ED - Teunissen, H AB -Soft particle materials are composed of discrete particles that can undergo large deformations without rupture. Most food products, many powders, colloidal pastes, vesicles and biological cells are soft particle systems. In order to model such materials, we present an efficient numerical approach combining an implicit formulation of the Material Point Method (MPM) and Contact Dynamics (CD) method. The MPM deals with bulk variables of an individual particle by discretizing it as a collection of material points, whereas the CD allows for the treatment of frictional contacts between particles. This model is applied for the simulation of the uniaxial compression of 2D soft-particle packings. The compaction is a nonlinear process in which new contacts are formed between particles and the contact areas increase. The change of particle shapes allows these materials to reach high packing fraction. We find that the contact specific surface, the orientation anisotropy and the aspect ratio of particles increase as a function of the packing fraction but at different rates. We also evidence the effect of friction, which favors strong stress chains and thus the elongation of particles, leading to larger values of the orientation anisotropy and the aspect ratio at a given level of packing fraction as compared to a frictionless particle packing.

JF - PROCEEDINGS OF THE 1ST INTERNATIONAL CONFERENCE ON THE MATERIAL POINT METHOD (MPM 2017) Book Series: Procedia Engineering PB - Elsevier Ltd. CY - JAN 10-13, 2017, Delft, NETHERLANDS VL - 175 JO - Procedia Engineering ER - TY - JOUR T1 - Nano-granular texture of cement hydrates JF - EPJ Web of Conferences Y1 - 2017 A1 - Katerina Ioannidou A1 - Franz-Josef Ulm A1 - Pierre E. Levitz A1 - Emanuela Del Gado A1 - Roland Jean-Marc Pellenq ED - Farhang Radjaï ED - Saeid Nezamabadi ED - Luding, S. ED - Jean-Yves Delenne AB -Mechanical behavior of concrete crucially depends on cement hydrates, the “glue” of cement. The design of high performance and more environmentally friendly cements demands a deeper understanding of the formation of the multiscale structure of cement hydrates, when they precipitate and densify. We investigate the precipitation and setting of nano-grains of cement hydrates using a combination of Monte Carlo and Molecular Dynamics numerical simulations and study their texture from nano up to the micron scale. We characterize the texture of cement hydrates using the local volume fraction distribution, the pore size distribution, the scattering intensity and the chord length distribution and we compare them with experiments. Our nano-granular model provides cement structure with realistic texture and mechanics and can be further used to investigate degradation mechanisms.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714015027 JO - EPJ Web Conf. ER - TY - JOUR T1 - Numerical insight into the micromechanics of jet erosion of a cohesive granular material JF - EPJ Web of Conferences Y1 - 2017 A1 - Cuellar, Pablo A1 - Benseghier, Zeyd A1 - Luu, Li-Hua A1 - Stéphane Bonelli A1 - Jean-Yves Delenne A1 - Farhang Radjaï A1 - Pierre Philippe ED - Saeid Nezamabadi ED - Luding, S. AB -Here we investigate the physical mechanisms behind the surface erosion of a cohesive granular soil induced by an impinging jet by means of numerical simulations coupling fluid and grains at the microscale. The 2D numerical model combines the Discrete Element and Lattice Boltzmann methods (DEM-LBM) and accounts for the granular cohesion with a contact model featuring a paraboloidal yield surface. Here we review first the hydrodynamical conditions imposed by the fluid jet on a solid granular packing, turning then the attention to the impact of cohesion on the erosion kinetics. Finally, the use of an additional subcritical debonding damage model based on the work of Silvani and co-workers provides a novel insight into the internal solicitation of the cohesive granular sample by the impinging jet.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714015017 JO - EPJ Web Conf. ER - TY - JOUR T1 - Numerical modeling of the tensile strength of a biological granular aggregate: Effect of the particle size distribution JF - EPJ Web of Conferences Y1 - 2017 A1 - Heinze, Karsta A1 - Frank, Xavier A1 - Valérie Lullien-Pellerina A1 - George, Matthieu A1 - Farhang Radjaï A1 - Jean-Yves Delenne ED - Saeid Nezamabadi ED - Luding, S. AB -Wheat grains can be considered as a natural cemented granular material. They are milled under high forces to produce food products such as flour. The major part of the grain is the so-called starchy endosperm. It contains stiff starch granules, which show a multi-modal size distribution, and a softer protein matrix that surrounds the granules. Experimental milling studies and numerical simulations are going hand in hand to better understand the fragmentation behavior of this biological material and to improve milling performance. We present a numerical study of the effect of granule size distribution on the strength of such a cemented granular material. Samples of bi-modal starch granule size distribution were created and submitted to uniaxial tension, using a peridynamics method. We show that, when compared to the effects of starch-protein interface adhesion and voids, the granule size distribution has a limited effect on the samples’ yield stress.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714008013 JO - EPJ Web Conf. ER - TY - JOUR T1 - Numerical study of the failure of materials embedding soft to hard particles JF - EPJ Web of Conferences Y1 - 2017 A1 - Frank, Xavier A1 - Jean-Yves Delenne A1 - Farhang Radjaï ED - Saeid Nezamabadi ED - Luding, S. AB -In this study, we use a bond-based peridynamic approach to investigate the mechanical strength and cracking of composite materials with spherical inclusions. The total volume fraction of particles and the particle-matrix toughness ratio were varied to cover a range of soft to hard inclusions. The mean particle damage was characterized together with crack patterns at a sub-particle scale. Three types of crack patterns are identified depending on the toughness ratio.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714002029 JO - EPJ Web Conf. ER - TY - JOUR T1 - Peridynamics simulation of the comminution of particles containing microcraks JF - EPJ Web of Conferences Y1 - 2017 A1 - Blanc, Nicolas A1 - Frank, Xavier A1 - Mayer-Laigle, Claire A1 - Farhang Radjaï A1 - Jean-Yves Delenne ED - Saeid Nezamabadi ED - Luding, S. ED - Jean-Yves Delenne AB -In this study, we rely on a ’bond-based’ peridynamic approach to investigate the strength and failure of 2D particles containing a collection of 1D microcracks. The mechanical tests were performed on disks under diametral compression. In an extensive parametric study, the distribution of microcracks was varied for different particle sizes. The evolution of yield stress with diameter and the probability of failure in terms of Weibull distributions are investigated in detail. Finally, by means of a floodfill algorithm, we analyze the variation of the mean fragment size as a function of the density of defects.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714007018 JO - EPJ Web Conf. ER - TY - JOUR T1 - The Potential of Mean Force concept for bridging (length and time) scales in the modeling of complex porous materials JF - EPJ Web of Conferences Y1 - 2017 A1 - Katerina Ioannidou A1 - Benoit Carrier A1 - Matthieu Vandamme A1 - Roland Jean-Marc Pellenq ED - Farhang Radjaï ED - Saeid Nezamabadi ED - Luding, S. ED - Jean-Yves Delenne AB -We introduce the concept of Potential of Mean Force, PMF, as a way to implement upscaling modeling from the nano-scale to micron-scale. A PMF is a free energy function representing in an effective way the interactions between objects (cement hydrates, clay platelets, etc.) at thermodynamics conditions. The PMF is therefore the key piece of information allowing to coarse-grained Physical-Chemistry information in a meso-scale model formulation. The use of PMF offers a huge computational advantage as it allows a straight up-scaling to the meso-scale while keeping essential interactions information that are the hallmark of Physical-Chemistry processes. Such a coarse-grained modeling integrates atomistic response into inter-particle potentials that fully propagate molecular scale information all the way to the meso-scale.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714001009 JO - EPJ Web Conf. ER - TY - JOUR T1 - Scaling behavior of immersed granular flows JF - EPJ Web of Conferences Y1 - 2017 A1 - L. Amarsid A1 - Jean-Yves Delenne A1 - Patrick Mutabaruka A1 - Yann Monerie A1 - Perales, F. A1 - Farhang Radjaï ED - Saeid Nezamabadi ED - Luding, S. AB -The shear behavior of granular materials immersed in a viscous fluid depends on fluid properties (viscosity, density), particle properties (size, density) and boundary conditions (shear rate, confining pressure). Using computational fluid dynamics simulations coupled with molecular dynamics for granular flow, and exploring a broad range of the values of parameters, we show that the parameter space can be reduced to a single parameter that controls the packing fraction and effective friction coefficient. This control parameter is a modified inertial number that incorporates viscous effects.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714009044 JO - EPJ Web Conf. ER - TY - JOUR T1 - Small solar system bodies as granular systems JF - EPJ Web of Conferences Y1 - 2017 A1 - Hestroffer, Daniel A1 - Adriano Campo Bagatín A1 - Losert, Wolfgang A1 - Opsomer, Eric A1 - Sánchez, Paul A1 - Scheeres, Daniel J. A1 - Staron, Lydie A1 - Taberlet, Nicolas A1 - Yano, Hajime A1 - Eggl, Siegfried A1 - Lecomte, Charles-Edouard A1 - Murdoch, Naomi A1 - Farhang Radjaï A1 - Richardson, Derek C. A1 - Salazar, Marcos A1 - Schwartz, Stephen R. A1 - Tanga, Paolo ED - Saeid Nezamabadi ED - Luding, S. ED - Jean-Yves Delenne AB -Asteroids and other Small Solar System Bodies (SSSBs) are currently of great scientific and even industrial interest. Asteroids exist as the permanent record of the formation of the Solar System and therefore hold many clues to its understanding as a whole, as well as insights into the formation of planetary bodies. Additionally, SSSBs are being investigated in the context of impact risks for the Earth, space situational awareness and their possible industrial exploitation (asteroid mining). In all these aspects, the knowledge of the geophysical characteristics of SSSB surface and internal structure are of great importance. Given their size, constitution, and the evidence that many SSSBs are not simple monoliths, these bodies should be studied and modelled as self-gravitating granular systems in general, or as granular systems in micro-gravity environments in particular contexts. As such, the study of the geophysical characteristics of SSSBs is a multi-disciplinary effort that lies at the crossroads between Granular Mechanics, Celestial Mechanics, Soil Mechanics, Aerospace Engineering and Computer Sciences.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714014011 JO - EPJ Web Conf. ER - TY - JOUR T1 - Strength of wet agglomerates of spherical particles: effects of friction and size distribution JF - EPJ Web of Conferences Y1 - 2017 A1 - Vo, Thanh-Trung A1 - Patrick Mutabaruka A1 - Jean-Yves Delenne A1 - Saeid Nezamabadi A1 - Farhang Radjaï ED - Luding, S. AB -We investigate the mechanical behavior of wet granular agglomerates composed of spherical particles by means of molecular dynamics simulations. The capillary cohesion force is modeled as an attraction force at the contact between two particles and expressed as an explicit function of the gap and volume of the liquid bridge. We are interested in the effect of the friction coefficient between primary particles. The agglomerates are subjected to diametrical compression tests. We find that the deformation is ductile involving particle rearrangements. However, a well-defined stress peak is observed and the peak stress is used as a measure of the compressive strength of the agglomerate. The strength increases with friction coefficient but levels off at friction coefficients above 0.4. Furthermore, the compressive strength is an increasing function of particle size span.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714008021 JO - EPJ Web Conf. ER - TY - JOUR T1 - Wall roughness and nonlinear velocity profiles in granular shear flows JF - EPJ Web of Conferences Y1 - 2017 A1 - Schuhmacher, Paul A1 - Farhang Radjaï A1 - Stéphane Roux ED - Saeid Nezamabadi ED - Luding, S. ED - Jean-Yves Delenne AB -Inhomogeneous velocity profiles in granular flows are well known from both experiments and simulations, and considered as a hallmark of nonlocal behavior. By means of extensive contact dynamics simulations, we show that the sigmoidal velocity profiles in 2D flows of rigid disks are controlled by the roughness of driving boundary walls. We find that the velocity profile becomes linear for a critical value of wall roughness up to an exponential decay close to the walls with a characteristic length that does not depend on the flow thickness and rate. We describe the velocity profiles by introducing a state parameter that carries wall perturbation. By assuming that the local shear rate is a linear function of the state parameter, we obtain an analytical expression that fits velocity profiles. In this model, the nonlinear velocity profiles are explained in terms of the effects of wall roughness as boundary condition for the state parameter.

VL - 140 UR - http://www.epj-conferences.org/10.1051/epjconf/201714003090 JO - EPJ Web Conf. ER - TY - JOUR T1 - Data analytics for simplifying thermal efficiency planning in cities JF - Journal of The Royal Society Interface Y1 - 2016 A1 - Mohammad Javad Abdolhosseini Qomi A1 - Noshadravan, Arash A1 - Sobstyl, Jake M. A1 - Toole, Jameson A1 - Ferreira, Joseph A1 - Roland Jean-Marc Pellenq A1 - Franz-Josef Ulm A1 - Gonzalez, Marta C. AB -More than 44% of building energy consumption in the USA is used for space heating and cooling, and this accounts for 20% of national CO2emissions. This prompts the need to identify among the 130 million households in the USA those with the greatest energy-saving potential and the associated costs of the path to reach that goal. Whereas current solutions address this problem by analysing each building in detail, we herein reduce the dimensionality of the problem by simplifying the calculations of energy losses in buildings. We present a novel inference method that can be used via a ranking algorithm that allows us to estimate the potential energy saving for heating purposes. To that end, we only need consumption from records of gas bills integrated with a building's footprint. The method entails a statistical screening of the intricate interplay between weather, infrastructural and residents' choice variables to determine building gas consumption and potential savings at a city scale. We derive a general statistical pattern of consumption in an urban settlement, reducing it to a set of the most influential buildings' parameters that operate locally. By way of example, the implications are explored using records of a set of (N= 6200) buildings in Cambridge, MA, USA, which indicate that retrofitting only 16% of buildings entails a 40% reduction in gas consumption of the whole building stock. We find that the inferred heat loss rate of buildings exhibits a power-law data distribution akin to Zipf's law, which provides a means to map an optimum path for gas savings per retrofit at a city scale. These findings have implications for improving the thermal efficiency of cities' building stock, as outlined by current policy efforts seeking to reduce home heating and cooling energy consumption and lower associated greenhouse gas emissions.

VL - 13 IS - 117 ER - TY - JOUR T1 - Bonded-cell model for particle fracture JF - Physical Review E Y1 - 2015 A1 - Duc-Hanh Nguyen A1 - Emilien Azéma A1 - Philippe Sornay A1 - Farhang Radjaï AB -Particle degradation and fracture play an important role in natural granular flows and in many applications of granular materials. We analyze the fracture properties of two-dimensional disklike particles modeled as aggregates of rigid cells bonded along their sides by a cohesive Mohr-Coulomb law and simulated by the contact dynamics method. We show that the compressive strength scales with tensile strength between cells but depends also on the friction coefficient and a parameter describing cell shape distribution. The statistical scatter of compressive strength is well described by the Weibull distribution function with a shape parameter varying from 6 to 10 depending on cell shape distribution. We show that this distribution may be understood in terms of percolating critical intercellular contacts. We propose a random-walk model of critical contacts that leads to particle size dependence of the compressive strength in good agreement with our simulation data.

VL - 91 IS - 2 JO - Phys. Rev. E ER - TY - JOUR T1 - Effect of curvature and confinement on the Casimir-Polder interaction JF - Physical Review A Y1 - 2015 A1 - Rodriguez-Lopez, Pablo A1 - Emig, Thorsten A1 - Noruzifar, Ehsan A1 - Zandi, Roya AB -Modifications of Casimir-Polder interactions due to confinement inside a cylindrical cavity and due to curvature in- and outside the cavity are studied. We consider a perfectly conducting cylindrical shell with a single particle (atom or macroscopic sphere) located next to its interior or exterior surface, or two atoms placed inside the shell. By employing the scattering approach, we obtain the particle-cavity interaction and the modification of the two-particle interaction due to the cavity. We consider both retardation and thermal effects. While for the atoms a dipole description is sufficient, for the macroscopic sphere we sum (numerically) over many multipole fluctuations to compute the interaction at short separations. In the latter limit we compare to the proximity approximation and a gradient expansion and find agreement. Our results indicate an confinement induced suppression of the force between atoms. General criteria for suppression and enhancement of Casimir interactions due to confinement are discussed.

VL - 91 IS - 1 JO - Phys. Rev. A ER - TY - JOUR T1 - Effects of shape and size polydispersity on strength properties of granular materials. JF - Phys Rev E Stat Nonlin Soft Matter Phys Y1 - 2015 A1 - Duc-Hanh Nguyen A1 - Emilien Azéma A1 - Philippe Sornay A1 - Farhang Radjaï AB -By means of extensive contact dynamics simulations, we analyze the combined effects of polydispersity both in particle size and in particle shape, defined as the degree of shape irregularity, on the shear strength and microstructure of sheared granular materials composed of pentagonal particles. We find that the shear strength is independent of the size span, but unexpectedly, it declines with increasing shape polydispersity. At the same time, the solid fraction is an increasing function of both the size span and the shape polydispersity. Hence, the densest and loosest packings have the same shear strength. At the scale of the particles and their contacts, we analyze the connectivity of particles, force transmission, and friction mobilization as well as their anisotropies. We show that stronger forces are carried by larger particles and propped by an increasing number of small particles. The independence of shear strength with regard to size span is shown to be a consequence of contact network self-organization, with the falloff of contact anisotropy compensated by increasing force anisotropy.

VL - 91 IS - 3 ER - TY - Generic T1 - Evolution of particle size distributions in crushable granular materials T2 - 3rd International Symposium on Geomechanics from Micro to Macro Y1 - 2015 A1 - Duc-Hanh Nguyen A1 - Emilien Azéma A1 - Farhang Radjaï A1 - Philippe Sornay ED - Kenichi Soga ED - Krishna Kumar ED - Giovanna Biscontin ED - Kuo, Matthew AB -

By means of the contact dynamics method together with a particle fracture model, in which the particles are cohesive aggregates of irreducible polygonal fragments, we investigate the evolution of particle size distribution in the process of uniaxial compaction of granular materials. The case of single particle breakup under compressive stress is used to test the method and the influence of discretization (number of irreducible fragments). We show that the breaking threshold of the granular assembly scales with the internal cohesion of the particles but it depends also on the initial size distribution and irregularity of polygonal particle shapes. The evolution of size distribution proceeds by consecutive periods of intense particle crushing, characterized by local shattering instability, and periods of little breaking activity. Starting with either monodisperse or power-law distribution of particle sizes, the latter evolves towards a broad distribution of the fragmented particles with a nearly power-law distribution in the range of intermediate particle sizes. Interestingly, a finite number of large particles survive despite ongoing crushing process due to the more homogeneous distribution of forces in the presence of small fragmented particles filling the pores between larger particles.

JF - 3rd International Symposium on Geomechanics from Micro to Macro PB - CRC Press CY - SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND VL - Geomechanics from Micro to Macro SN - 978-1-138-02707-7 ER - TY - JOUR T1 - Implicit frictional-contact model for soft particle systems JF - Journal of the Mechanics and Physics of Solids Y1 - 2015 A1 - Saeid Nezamabadi A1 - Farhang Radjaï A1 - Julien Averseng A1 - Jean-Yves Delenne AB -We introduce a novel numerical approach for the simulation of soft particles interacting via frictional contacts. This approach is based on an implicit formulation of the Material Point Method, allowing for large particle deformations, combined with the Contact Dynamics method for the treatment of unilateral frictional contacts between particles. This approach is both precise due to the treatment of contacts with no regularization and artificial damping parameters, and robust due to implicit time integration of both bulk degrees of freedom and relative contact velocities at the nodes representing the contact points. By construction, our algorithm is capable of handling arbitrary particle shapes and deformations. We illustrate this approach by two simple 2D examples: a Hertz contact and a rolling particle on an inclined plane. We also investigate the compaction of a packing of circular particles up to a solid fraction well above the jamming limit of hard particles. We find that, for the same level of deformation, the solid fraction in a packing of frictional particles is above that of a packing of frictionless particles as a result of larger particle shape change.

VL - 83 JO - Journal of the Mechanics and Physics of Solids ER - TY - Generic T1 - Micromechanical analysis of the surface erosion of a cohesive soil by means of a coupled LBM-DEM model T2 - IV International Conference on Particle-based Methods (PARTICLES 2015) Y1 - 2015 A1 - Cuellar, Pablo A1 - Pierre Philippe A1 - Stéphane Bonelli A1 - Benahmed, Nadia A1 - Brunier-Coulin, Florian A1 - Jeff Ngoma A1 - Jean-Yves Delenne A1 - Farhang Radjaï ED - Onate, E ED - Bischoff, M ED - Owen, DRJ KW - Cohesion KW - DEM KW - LBM KW - Surface erosion AB -The elementary mechanisms driving the ubiquitous surface erosion of cohesive geomaterials can be analysed from a micromechanical perspective combining well-known numerical techniques. Here, a coupled model combining the Discrete Element and Lattice Boltzmann methods (DEM-LBM) provides an insight into the solid-fluid interaction during the transient erosion caused by a vertical fluid jet impinging on the surface of a granular assembly. The brittle cementation providing cohesion between the solid grains is described here by means of a simple bond model with a single-parameter yield surface. The initial topology of the surface erosion tends to mimic the profile of fluid velocity directly above the soil surface. We find that both the rate of erosion and the magnitude of eroded mass depend directly on the micromechanical strength of the single solid bonds.

JF - IV International Conference on Particle-based Methods (PARTICLES 2015) PB - International Center for Numerical Methods in Engineering (CIMNE) CY - SEP 28-30 2015 Barcelona, SPAIN VL - PARTICLE-BASED METHODS IV-FUNDAMENTALS AND APPLICATIONS UR - https://hal.archives-ouvertes.fr/hal-01269324 ER - TY - Generic T1 - Transient regime to fluidized chimney within a granular bed by means of a 2D DEM/LBM modeling T2 - IV International Conference on Particle-based Methods (PARTICLES 2015) Y1 - 2015 A1 - Jeff Ngoma A1 - Pierre Philippe A1 - Stéphane Bonelli A1 - Cuellar, Pablo A1 - Jean-Yves Delenne A1 - Farhang Radjaï ED - Onate, E ED - Bischoff, M ED - Owen, DRJ KW - DEM KW - Fluidization KW - Granular Materials KW - LBM AB -Beyond a given threshold, an upward fluid flow at constant flowrate, injected through a small size section, is able to generate a fluidization along a vertical chimney over the entire height of a granular assembly. Fluidization is first initiated in the immediate vicinity of the injection hole and then the fluidized zone grows gradually until reaching the upper surface of the granular packing. In this work, we present numerical results on the kinetics of chimney fluidization in an immersed granular bed produced with two-dimensional simulations coupling the Discrete Element and Lattice Boltzmann Methods (DEM-LBM). A parametric study is carried out with 11 different sets of physical parameters and analyzed based on spatio-temporal diagrams. Then a dimensional analysis allows finding general scaling laws for both threshold and growth rate of the fluidized zone by use of two dimensionless numbers, namely Reynolds and Archimedes numbers, while quite simple empirical relationships can also be proposed.

JF - IV International Conference on Particle-based Methods (PARTICLES 2015) PB - International Center for Numerical Methods in Engineering (CIMNE) CY - SEP 28-30 2015 Barcelona, SPAIN VL - PARTICLE-BASED METHODS IV-FUNDAMENTALS AND APPLICATIONS UR - https://hal.archives-ouvertes.fr/hal-01269325 ER - TY - JOUR T1 - Effect of size polydispersity versus particle shape in dense granular media JF - Physical Review E Y1 - 2014 A1 - Duc-Hanh Nguyen A1 - éma, Emilien A1 - Farhang Radjaï A1 - Philippe Sornay AB -We present a detailed analysis of the morphology of granular systems composed of frictionless pentagonal particles by varying systematically both the size span and particle shape irregularity, which represent two polydispersity parameters of the system. The microstructure is characterized in terms of various statistical descriptors such as global and local packing fractions, radial distribution functions, coordination number, and fraction of floating particles. We find that the packing fraction increases with the two parameters of polydispersity, but the effect of shape polydispersity for all the investigated structural properties is significant only at low size polydispersity where the positional and/or orientational ordering of the particles prevail. We focus in more detail on the class of side/side contacts, which is the interesting feature of our system as compared to a packing of disks. We show that the proportion of such contacts has weak dependence on the polydispersity parameters. The side- side contacts do not percolate but they define clusters of increasing size as a function of size polydispersity and decreasing size as a function of shape polydispersity. The clusters have anisotropic shapes but with a decreasing aspect ratio as polydispersity increases. This feature is argued to be a consequence of strong force chains (forces above the mean), which are mainly captured by side-side contacts. Finally, the force transmission is intrinsically multiscale, with a mean force increasing linearly with particle size.

VL - 90 IS - 1 JO - Phys. Rev. E ER - TY - Generic T1 - Geomechanics from Micro to MacroInteraction between two localized fluidization cavities in granular media : Experiments and numerical simulation T2 - 3rd International Symposium on Geomechanics from Micro to Macro Y1 - 2014 A1 - Jeff Ngoma A1 - Pierre Philippe A1 - Stéphane Bonelli A1 - Jean-Yves Delenne A1 - Farhang Radjaï ED - Kenichi Soga ED - Krishna Kumar ED - Giovanna Biscontin ED - Kuo, Matthew AB -In this work, we present experimental and numerical results on the interaction between two localized fluidization cavities in an immersed granular packing. According to the gap between the two locally injected upward fluid flows, each fluidized cavity will evolve independently of the another, or conversely, the two cavities can interact with each other: they merge and eventually behave like a single cavity. Combined optical techniques are used for visualization of particle motion inside the granular media (Refractive Index-Matching between liquid and beads and Planar Laser-Induced Fluorescence), the experimental results are compared to a two-dimensional simulation based on coupled Discrete Element and Lattice Boltzmann Methods (DEM-LBM).

JF - 3rd International Symposium on Geomechanics from Micro to Macro PB - CRC Press CY - SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND VL - Geomechanics from Micro to Macro SN - 978-1-138-02707-7 ER - TY - Generic T1 - Modelling soft-particle materials T2 - 3rd International Symposium on Geomechanics from Micro to Macro Y1 - 2014 A1 - Saeid Nezamabadi A1 - Farhang Radjaï A1 - Julien Averseng ED - Kenichi Soga ED - Krishna Kumar ED - Giovanna Biscontin AB -Soft-particle materials include colloidal pastes, vesicles, many powders, microgels and suspensions. They share the common feature of being composed of particles that can undergo large deformations without rupture. For the simulation of such materials, we present a modelling approach based on an implicit formulation of the Material Point Method (MPM) interfaced with the Contact Dynamics (CD) method for the treatment of frictional contacts between particles. Each particle is discretized as a collection of material points. The information carried by the material points is projected onto a background mesh, where equations of motion are solved. The mesh solution is then used to update the material points. The implicit formulation of MPM allows for unconditional numerical stability and efficient coupling with implicit treatment of unilateral contacts and friction between the particles by the CD method. We use this model to analyse the compaction process of 2D soft-particle packings. The packing can reach high solid fractions by particle shape change and still flow plastically. The compaction is a nonlinear process in which new contacts are formed between particles and the contact areas increase. We find that the evolution of the packing fraction is a slow logarithmic function of the driving stress as a consequence of increasing contact area. We also evidence the effect of friction, which favours strong stress chains and thus the elongation of particles, leading to a larger packing fraction at a given level of compressive stress as compared to a frictionless particle packing.

JF - 3rd International Symposium on Geomechanics from Micro to Macro PB - CRC Press CY - SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND VL - Geomechanics from Micro to Macro UR - http://prodinra.inra.fr/record/370208 ER - TY - JOUR T1 - Some micromechanical aspects of failure in granular materials based on second-order work JF - Comptes Rendus Mécanique Y1 - 2014 A1 - François Nicot A1 - Hadda, Nejib A1 - Sibille, Luc A1 - Farhang Radjaï A1 - Hicher, Pierre-Yves A1 - Darve, Félix AB -This paper discusses the notion of failure in a granular assembly by examining the key microstructural mechanisms which are most likely to trigger the nucleation and propagation of instabilities within a granular material. For this purpose, the key variable to predict the occurrence of failure, known as second-order work, is expressed from variables on the grain scale. The local behaviour incidents (where contacts may open or slide), compared to the global response of the assembly, are analysed by two approaches. First, numerical computations made by a discrete element model confirm the microscopic definition of the second-order work. Secondly, a micromechanical model, based on a homogenization procedure, relating the macroscopic behaviour to microscopic ingredients, namely contact planes, points to a close link between the occurrence of failure on the macroscopic scale as well as on the contact planes.

VL - 342 IS - 3 JO - Comptes Rendus Mécanique ER - TY - JOUR T1 - Ultrahigh interlayer friction in multiwalled boron nitride nanotubes JF - Nat Mater Y1 - 2014 A1 - Nigues, A. A1 - A. Siria A1 - Vincent, P. A1 - Poncharal, P. A1 - Lydéric Bocquet AB -Friction at the nanoscale has revealed a wealth of behaviours that depart strongly from the long-standing macroscopic laws of Amontons–Coulomb^{1, 2}. Here, by using a ‘Christmas cracker’-type of system in which a multiwalled nanotube is torn apart between a quartz-tuning-fork-based atomic force microscope (TF–AFM) and a nanomanipulator, we compare the mechanical response of multiwalled carbon nanotubes (CNTs) and multiwalled boron nitride nanotubes (BNNTs) during the fracture and telescopic sliding of the layers. We found that the interlayer friction for insulating BNNTs results in ultrahigh viscous-like dissipation that is proportional to the contact area, whereas for the semimetallic CNTs the sliding friction vanishes within experimental uncertainty. We ascribe this difference to the ionic character of the BN, which allows charge localization. The interlayer viscous friction of BNNTs suggests that BNNT membranes could serve as extremely efficient shock-absorbing surfaces.

Four pure silica zeolites, chabazite (CHA-structure type) and SSZ-23 (STT-structure type) with cage-like structure and silicalite-1 (MFI-structure type) and beta (^{∗}BEA-structure type) with channel structure, were synthesized and fully characterized. Their sorption properties were examined using gravimetric method combined with Grand Canonical Monte Carlo simulations (GCMC). Of particular interest is the large difference in the adsorption rates of *n*-hexane, *p*-xylene and acetone observed for these zeosils at 25, 75 and 150 °C. As expected, in most cases, a decrease in the adsorption capacity is observed with increasing the molar volume of the used probe molecule and the temperature. An exception is observed for the pure silica CHA-type zeolite due to its small pore size which prevents molecules from entering its porosity. However, at higher temperature, the window size widens slightly and allows *n*-hexane and acetone, which have kinetic diameter close to the pore opening, to enter easily in chabazite. As a result, for this zeosil, an increase in the adsorption capacity compared to that obtained at 25 °C is observed. All these zeosils are promising for technological uses in car exhaust gas decontamination.

This paper presents conditions of initiation and development of failure in granular materials through a twodimensional discrete element model. General condition for the effective development of failure and its physical characteristics are recalled. Then relation between failure and the second order work expressed in terms of microscopic variables is discussed. Eventually, correspondence between a localized mode of failure marked with shear band patterns and space distribution of negative values of microscopic second-order work is investigated.

JF - 7th International Conference on Micromechanics of Granular Media (Powders and Grains) PB - AIP CY - JUL 08-12 2013 Sydney, AUSTRALIA VL - Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013 ER - TY - Generic T1 - A benchmark for particle shape dependence T2 - 7th International Conference on Micromechanics of Granular Media (Powders and Grains) Y1 - 2013 A1 - Gael Combe A1 - Cécile Nouguier-Lehon A1 - Emilien Azéma A1 - Krzysztof Szarf A1 - Baptiste Saint-Cyr A1 - Marie Chaze A1 - Farhang Radjaï A1 - Pascal Villard A1 - Jean-Yves Delenne A1 - Vincent Richefeu A1 - Philippe Sornay A1 - Charles Voivret A1 - CEGEO Group ED - Yu, A ED - Dong, K ED - Yang, R AB -Particle shape is a major parameter for the space-filling and strength properties of granular materials. For a systematic investigation of shape effect, a numerical benchmark test was set up within a collaborative group using different numerical methods and particles of various shape characteristics such as elongation, angularity and nonconvexity. Extensive 2D shear simulations were performed in this framework and the shear strength and packing fraction were compared for different shapes. We show that the results may be analyzed in terms of a low-order shape parameter η describing the degree of distortion from a perfectly circular shape. In particular, the shear strength is an increasing function of η with nearly the same trend for all shapes, the differences being of second order compared to η. We also observe a nontrivial behavior of packing fraction which, for all our simulated shapes, increases with η from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as η is further increased. Finally, the analysis of contact forces for the same value of η leads to very similar statistics regardless of our specific particle shapes.

JF - 7th International Conference on Micromechanics of Granular Media (Powders and Grains) PB - AIP CY - JUL 08-12 2013 Sydney, AUSTRALIA VL - Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013 ER - TY - JOUR T1 - Micromechanical analysis of second order work in granular media JF - Granular Matter Y1 - 2013 A1 - Hadda, Nejib A1 - François Nicot A1 - Bourrier, Franck A1 - Sibille, Luc A1 - Farhang Radjaï A1 - Darve, Félix AB -This paper examines instabilities in granular materials from a microscopic point of view through numerical simulations conducted using a discrete element method on two three-dimensional specimens. The detection and the tracking of grain scale deformation mechanisms constitute the key point for a better understanding the failure process and puzzling out what lies behind the vanishing of the macroscopic second order work. For this purpose, the second order work from microscopic variables, involving contact force and branch vector, was introduced and tracked numerically. Then, all contacts depicting negative values of the second order work were deeply investigated, especially their spatial distribution (homogeneity, agglomeration, dispersion

The accuracy and the comprehensiveness of any pavement life-cycle assessment are limited by the ability of the supporting science to quantify the environmental impact. Pavement-vehicle interaction represents a significant knowledge gap that has important implications for many pavement life-cycle assessment studies. In the current study, the authors assumed that a mechanistic model that linked pavement structure and properties to fuel consumption could contribute to closing the uncertainty gap of pavement-vehicle interaction in life-cycle assessment of pavements. The simplest mechanistic pavement model, a Bernoulli-Euler beam on a viscoelastic foundation subjected to a moving load, was considered. Wave propagation properties derived from falling weight deflectometer time history data of FHWA's Long-Term Pavement Performance program were used to calibrate top-layer and substrate moduli for various asphalt and concrete systems. The model was validated against recorded deflection data. The mechanistic response was used to determine gradient force and rolling resistance to link deflection to vehicle fuel consumption. A comparison with independent field data provided realistic order-of-magnitude estimates of fuel consumption related to pavement-vehicle interaction as predicted by the model.

IS - 2306 JO - Transportation Research Record: Journal of the Transportation Research Board ER - TY - Generic T1 - Microscopic Origins of Shear Strength in Packings Composed of Elongated Particles T2 - 9th International Workshop on Bifurcation and Degradation in Geomaterials (IWBDG 2011) Y1 - 2012 A1 - Emilien Azéma A1 - Farhang Radjaï ED - Stéphane Bonelli ED - Dascalu, Cristian ED - François Nicot KW - Elongated particles KW - Fabric properties KW - force transmission KW - Harmonic decomposition AB -We investigate the rheology, force transmission and texture of granular materials composed of elongated particles by means of contact dynamics simulations. The particles have a rounded-cap rectangular (RCR) shape described by a single elongation parameter varying from 0 for a circular particle to 1 for an infinitely thin or long particle. We study the quasi-static behavior, structural and force anisotropies as a function of the elongation parameter for packings submitted to biaxial compression. The shear strength is found to increase linearly with this parameter whereas the solid fraction both at the initial isotropic state and in the critical state is nonmonotonous. We show that for these elongated particles a harmonic decomposition of the stress tensor provides a fairly good approximation of the internal state. Our data suggest that the increase of shear strength with reflects both enhanced friction mobilization and anisotropic particle orientation as the elongation of the particles increases.

JF - 9th International Workshop on Bifurcation and Degradation in Geomaterials (IWBDG 2011) CY - MAY 23-26 2011 Porquerolles, FRANCE VL - Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS UR - https://hal.archives-ouvertes.fr/hal-00686728 ER - TY - JOUR T1 - Particle shape dependence in 2D granular media JF - EPL (Europhysics Letters) Y1 - 2012 A1 - Baptiste Saint-Cyr A1 - Krzysztof Szarf A1 - Charles Voivret A1 - Emilien Azéma A1 - Vincent Richefeu A1 - Jean-Yves Delenne A1 - Gael Combe A1 - Cécile Nouguier-Lehon A1 - Pascal Villard A1 - Philippe Sornay A1 - Marie Chaze A1 - Farhang Radjaï AB -Particle shape is a key to the space-filling and strength properties of granular matter. We consider a shape parameter

We rely on 3D simulations based on the Lattice Element Method (LEM) to analyze the failure of porous granular aggregates under tensile loading. We investigate crack growth by considering the number of broken bonds in the particle phase as a function of the matrix volume fraction and particle-matrix adhesion. Three regimes are evidenced, corresponding to no particle damage, particle abrasion and particle fragmentation, respectively. We also show that the probability density of strong stresses falls off exponentially at high particle volume fractions where a percolating network of jammed particles occurs. Decreasing the matrix volume fraction leads to increasingly broader stress distribution and hence a higher stress concentration. Our findings are in agreement with 2D results previously reported in the literature.

JF - 9th International Workshop on Buifurcation and Degradation in Geomaterials (IWBDG 2011) PB - Springer Netherlands CY - MAY 23-26 2011 Porquerolles, FRANCE VL - Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS SN - 978-94-007-1420-5 ER - TY - Generic T1 - Onset of Immersed Granular Avalanches by DEM-LBM Approach T2 - 9th International Workshop on Buifurcation and Degradation in Geomaterials (IWBDG 2011) Y1 - 2011 A1 - Jean-Yves Delenne A1 - Mansouri, M. A1 - Farhang Radjaï A1 - Moulay Saïd El Youssoufi A1 - Seridi, A. ED - Stéphane Bonelli ED - Dascalu, Cristian ED - François Nicot AB -We present 3D grain-fluid simulations based on the discrete element method interfaced with the lattice Boltzmann method and applied to investigate the initiation of underwater granular flows. We prepare granular beds of 800 spherical grains with different values of the initial solid fraction in a biperiodic rectangular box. In order to trigger an avalanche, the bed is instantaneously tilted to a finite slope angle above the maximum angle of stability. We simulate the dynamics of the transient flow for different solid fractions. In agreement with the experimental work of Iverson (Water Resour Res 36(7):1897–1910, 2000) and Pailha et al. (Phys Fluids 20(11):111701, 2008), we find that the flow onset is controlled by the initial solid fraction.

JF - 9th International Workshop on Buifurcation and Degradation in Geomaterials (IWBDG 2011) PB - Springer Netherlands CY - MAY 23-26 2011 Porquerolles, FRANCE VL - Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS SN - 978-94-007-1420-5 ER -