@article {667, title = {Parallel implicit contact algorithm for soft particle systems}, journal = {Computer Physics Communications}, volume = {237}, year = {2019}, month = {Apr-01-2019}, pages = {17 - 25}, abstract = {

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.

}, issn = {00104655}, doi = {10.1016/j.cpc.2018.10.030}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0010465518303904}, author = {Saeid Nezamabadi and Frank, Xavier and Jean-Yves Delenne and Julien Averseng and Farhang Radja{\"\i}} } @article {533, title = {Mechanical strength of wet particle agglomerates}, journal = {Mechanics Research Communications}, volume = {92}, year = {2018}, month = {Sep-2018}, pages = {1 - 7}, abstract = {

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.

Fig. 1. Schematic drawing of the forces acting on particle i by a contacting particle j{\textellipsis}

Fig. 2. Schematic representation of diametrical compression test (a), and snapshots of{\textellipsis}

Fig. 3. Snapshot of a granule under diametrical compression for α=1

Fig. 4. Vertical strength σzz normalized by the reference stress σc for different{\textellipsis}

Fig. 5. Normalized plastic strength of the granule for several values of the debonding{\textellipsis}

Fig. 6. Normalized plastic strength σp/σc of the granules for different values of the{\textellipsis}

Fig. 7. The initial wet coordination number Z0 of the granules for different values of{\textellipsis}

Fig. 8. The prefactor η in Eq

Fig. 9. The ZΦs in Eq

}, issn = {00936413}, doi = {10.1016/j.mechrescom.2018.07.003}, url = {https://www-sciencedirect-com.libproxy.mit.edu/science/article/pii/S0093641318301216}, author = {Vo, Thanh-Trung and Patrick Mutabaruka and Saeid Nezamabadi and Jean-Yves Delenne and Izard, Edouard and Roland Jean-Marc Pellenq and Farhang Radja{\"\i}} } @article {627, title = {Multiscale modeling for bioresources and bioproducts}, journal = {Innovative Food Science \& Emerging Technologies}, volume = {46}, year = {2018}, month = {Avr-2018}, pages = {41 - 53}, abstract = {

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.

}, issn = {14668564}, doi = {10.1016/j.ifset.2017.09.015}, url = {https://linkinghub.elsevier.com/retrieve/pii/S1466856417302230}, author = {Barnabe, M. and Blanc, Nicolas and Chabin, T. and Jean-Yves Delenne and Duri, A. and Frank, Xavier and Hugouvieux, V. and Lutton, E. and Mabille, F. and Saeid Nezamabadi and Perrot, N. and Farhang Radja{\"\i} and Ruiz, T. and Tonda, A.} } @article {600, title = {Cohesive strength of iron ore granules}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 08020}, abstract = {

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.

}, doi = {10.1051/epjconf/201714008020}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714008020}, author = {Contreras, Rafael Jaimes and Berger, Nicolas and Izard, Edouard and Douce, Jean-Fran{\c c}ois and Koltsov, Alexey and Jean-Yves Delenne and Emilien Az{\'e}ma and Saeid Nezamabadi and van Loo, Fr{\'e}d{\'e}ric and Roland Jean-Marc Pellenq and Farhang Radja{\"\i}}, editor = {Luding, S.} } @article {602, title = {Compaction of granular materials composed of deformable particles}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 05013}, abstract = {

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.

}, doi = {10.1051/epjconf/201714005013}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714005013}, author = {Thanh Hai Nguyen and Saeid Nezamabadi and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Luding, S.} } @article {601, title = {Effect of particle size distribution on 3D packings of spherical particles}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 02030}, abstract = {

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 of the largest size to the smallest size. We find that, up to = 5, the packing fraction is a nearly linear function of . 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 . 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.

}, doi = {10.1051/epjconf/201714002030}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714002030}, author = {Taiebat, Mahdi and Patrick Mutabaruka and Roland Jean-Marc Pellenq and Farhang Radja{\"\i}}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {606, title = {Modeling root growth in granular soils: effects of root stiffness and packing fraction}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 14013}, abstract = {

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.

}, doi = {10.1051/epjconf/201714014013}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714014013}, author = {Fakih, Mahmoud and Jean-Yves Delenne and Farhang Radja{\"\i} and Fourcaud, Thierry}, editor = {Saeid Nezamabadi and Luding, S.} } @article {265, title = {Modeling soft granular materials}, journal = {Granular Matter}, volume = {19}, year = {2017}, month = {Jun-17-2017}, pages = {Article Number: 8}, abstract = {

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.

}, issn = {1434-5021}, doi = {10.1007/s10035-016-0689-y}, author = {Saeid Nezamabadi and Thanh Hai Nguyen and Jean-Yves Delenne and Farhang Radja{\"\i}} } @proceedings {337, title = {MPM with Frictional Contact for Application to Soft Particulate Materials}, journal = {PROCEEDINGS OF THE 1ST INTERNATIONAL CONFERENCE ON THE MATERIAL POINT METHOD (MPM 2017) Book Series: Procedia Engineering }, volume = {175}, year = {2017}, month = {Mar-23-2017}, pages = {141 - 147}, publisher = {Elsevier Ltd.}, address = {JAN 10-13, 2017, Delft, NETHERLANDS}, abstract = {

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.

}, issn = {18777058}, doi = {10.1016/j.proeng.2017.01.044}, author = {Saeid Nezamabadi and Thanh Hai Nguyen and Jean-Yves Delenne and Julien Averseng and Frank, Xavier and Farhang Radja{\"\i}}, editor = {Rohe, A and Kenichi Soga and Teunissen, H} } @article {623, title = {Nano-granular texture of cement hydrates}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 15027}, abstract = {

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.

}, doi = {10.1051/epjconf/201714015027}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714015027}, author = {Katerina Ioannidou and Franz-Josef Ulm and Pierre E. Levitz and Emanuela Del Gado and Roland Jean-Marc Pellenq}, editor = {Farhang Radja{\"\i} and Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {604, title = {Numerical insight into the micromechanics of jet erosion of a cohesive granular material}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 15017}, abstract = {

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.

}, doi = {10.1051/epjconf/201714015017}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714015017}, author = {Cuellar, Pablo and Benseghier, Zeyd and Luu, Li-Hua and St{\'e}phane Bonelli and Jean-Yves Delenne and Farhang Radja{\"\i} and Pierre Philippe}, editor = {Saeid Nezamabadi and Luding, S.} } @article {608, title = {Numerical modeling of the tensile strength of a biological granular aggregate: Effect of the particle size distribution}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 08013}, abstract = {

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.

}, doi = {10.1051/epjconf/201714008013}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714008013}, author = {Heinze, Karsta and Frank, Xavier and Val{\'e}rie Lullien-Pellerina and George, Matthieu and Farhang Radja{\"\i} and Jean-Yves Delenne}, editor = {Saeid Nezamabadi and Luding, S.} } @article {603, title = {Numerical study of the failure of materials embedding soft to hard particles}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 02029}, abstract = {

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.

}, doi = {10.1051/epjconf/201714002029}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714002029}, author = {Frank, Xavier and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Saeid Nezamabadi and Luding, S.} } @article {597, title = {Peridynamics simulation of the comminution of particles containing microcraks}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 07018}, abstract = {

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.

}, doi = {10.1051/epjconf/201714007018}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714007018}, author = {Blanc, Nicolas and Frank, Xavier and Mayer-Laigle, Claire and Farhang Radja{\"\i} and Jean-Yves Delenne}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {622, title = {The Potential of Mean Force concept for bridging (length and time) scales in the modeling of complex porous materials}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 01009}, abstract = {

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.

}, doi = {10.1051/epjconf/201714001009}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714001009}, author = {Katerina Ioannidou and Benoit Carrier and Matthieu Vandamme and Roland Jean-Marc Pellenq}, editor = {Farhang Radja{\"\i} and Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {607, title = {Scaling behavior of immersed granular flows}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 09044}, abstract = {

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.

}, doi = {10.1051/epjconf/201714009044}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714009044}, author = {L. Amarsid and Jean-Yves Delenne and Patrick Mutabaruka and Yann Monerie and Perales, F. and Farhang Radja{\"\i}}, editor = {Saeid Nezamabadi and Luding, S.} } @article {605, title = {Small solar system bodies as granular systems}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 14011}, abstract = {

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.

}, doi = {10.1051/epjconf/201714014011}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714014011}, author = {Hestroffer, Daniel and Adriano Campo Bagat{\'\i}n and Losert, Wolfgang and Opsomer, Eric and S{\'a}nchez, Paul and Scheeres, Daniel J. and Staron, Lydie and Taberlet, Nicolas and Yano, Hajime and Eggl, Siegfried and Lecomte, Charles-Edouard and Murdoch, Naomi and Farhang Radja{\"\i} and Richardson, Derek C. and Salazar, Marcos and Schwartz, Stephen R. and Tanga, Paolo}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {599, title = {Strength of wet agglomerates of spherical particles: effects of friction and size distribution}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 08021}, abstract = {

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.

}, doi = {10.1051/epjconf/201714008021}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714008021}, author = {Vo, Thanh-Trung and Patrick Mutabaruka and Jean-Yves Delenne and Saeid Nezamabadi and Farhang Radja{\"\i}}, editor = {Luding, S.} } @article {598, title = {Wall roughness and nonlinear velocity profiles in granular shear flows}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 03090}, abstract = {

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.

}, doi = {10.1051/epjconf/201714003090}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714003090}, author = {Schuhmacher, Paul and Farhang Radja{\"\i} and St{\'e}phane Roux}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {271, title = {Implicit frictional-contact model for soft particle systems}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {83}, year = {2015}, month = {Oct-2015}, pages = {72 - 87}, abstract = {

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.

}, issn = {00225096}, doi = {10.1016/j.jmps.2015.06.007}, author = {Saeid Nezamabadi and Farhang Radja{\"\i} and Julien Averseng and Jean-Yves Delenne} } @proceedings {342, title = {Modelling soft-particle materials}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2014}, month = {Aug-26-2014}, pages = {43-48}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

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.

}, url = {http://prodinra.inra.fr/record/370208}, author = {Saeid Nezamabadi and Farhang Radja{\"\i} and Julien Averseng}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin} }