@article {594, title = {Investigation of mixed ionic/nonionic building blocks for the dual templating of macro-mesoporous silica}, journal = {Journal of Colloid and Interface Science}, volume = {533}, year = {2019}, month = {Jan-01-2019}, pages = {385 - 400}, abstract = {

Traditional porous monoliths Si(HIPE) (High Internal Phase Emulsion), prepared from the Tetradecyltrimethylammonium Bromide (TTAB)/dodecane/water system, offer high specific surface area, mainly due to microporosity. Aside, mesoporous materials SBA-15, prepared from Pluronic P123, have a high specific surface area, but are obtained as powder, which limits their applications. Starting from the mixed TTAB-P123 surfactant, it is expected to tune the mesoporosity of Si(HIPE), while keeping their monolithic character.

The ternary TTAB/P123/water phase diagram was established by varying the weight ratio between these two surfactants. The micellar structure as well as the structural parameters of the liquid crystal domains were determined by SAXS (Small Angle X-ray Scattering). The effect of dodecane solubilization was also investigated and concentrated emulsions were formulated from the (P123/TTAB)/dodecane/ water systems. After this soft matter dedicated study, the acquired knowledge was transferred toward the hierarchical porous silica generations, where the sol-gel process is involved.

Mixing P123 with TTAB, macro-mesoporous monolithic silica with an enhanced contribution of the specific surface area due to mesoporosity can be prepared. The variation of the TTAB/P123 weight ratio allows controlling the porosity at the mesoscale. Moreover, the macroporosity can be tuned by changing the preparation method, by mixing either the two micellar solutions or directly the two surfactants prior the emulsification process. (C) 2018 Elsevier Inc. All rights reserved.

}, issn = {00219797}, doi = {10.1016/j.jcis.2018.08.068}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0021979718309883}, author = {Roucher, Armand and Emo, Melanie and Vibert, Francois and Stebe, Marie-Jose and Schmitt, Veronique and Jonas, Florian and Backov, Renal and Blin, Jean-Luc} } @article {666, title = {Modified Szeg{\"o}{\textendash}Widom Asymptotics for Block Toeplitz Matrices with Zero Modes}, journal = {Journal of Statistical Physics}, volume = {174}, year = {2019}, month = {Jan-2019}, pages = {28 - 39}, abstract = {

The Szego-Widom theorem provides an expression for the determinant of block Toeplitz matrices in the asymptotic limit of large matrix dimension n. We show that the presence of zero modes, i.e, eigenvalues that vanish as n, ||\<1, when n, requires a modification of the Szego-Widom theorem. A new asymptotic expression for the determinant of a certain class of block Toeplitz matrices with one pair of zero modes is derived. The result is inspired by one-dimensional topological superconductors, and the relation with the latter systems is discussed.

}, issn = {0022-4715}, doi = {10.1007/s10955-018-2177-8}, url = {http://link.springer.com/10.1007/s10955-018-2177-8}, author = {Basor, E. and Dubail, Jerome and Emig, Thorsten and Santachiara, Raoul} } @article {610, title = {A minimal power model for human running performance}, journal = {PLOS ONE}, volume = {13}, year = {2018}, month = {Nov-16-2018}, pages = {e0206645}, abstract = {

Models for human running performances of various complexities and underlying principles have been proposed, often combining data from world record performances and bio-energetic facts of human physiology. The purpose of this work is to develop a novel, minimal and universal model for human running performance that employs a relative metabolic power scale. The main component is a self-consistency relation for the time dependent maximal power output. The analytic approach presented here is the first to derive the observed logarithmic scaling between world (and other) record running speeds and times from basic principles of metabolic power supply. Our hypothesis is that various female and male record performances (world, national) and also personal best performances of individual runners for distances from 800m to the marathon are excellently described by this model. Indeed, we confirm this hypothesis with mean errors of (often much) less than 1\%. The model defines endurance in a way that demonstrates symmetry between long and short racing events that are separated by a characteristic time scale comparable to the time over which a runner can sustain maximal oxygen uptake. As an application of our model, we derive personalized characteristic race speeds for different durations and distances.

}, keywords = {ENERGY-COST; OXYGEN-UPTAKE; ATHLETIC RECORDS; ECONOMY; RUNNERS; RUN; ENDURANCE; MARATHON; EXERCISE; EXHAUSTION}, doi = {10.1371/journal.pone.0206645}, url = {http://dx.plos.org/10.1371/journal.pone.0206645}, author = {Mulligan, Matthew and Adam, Guillaume and Emig, Thorsten}, editor = {Piknova, Barbora} } @article {574, title = {Role of City Texture in Urban Heat Islands at Nighttime}, journal = {Physical Review Letters}, volume = {120}, year = {2018}, month = {Mar-09-2018}, pages = {Article Number: 108701 }, abstract = {

An urban heat island (UHI) is a climate phenomenon that results in an increased air temperature in cities when compared to their rural surroundings. In this Letter, the dependence of an UHI on urban geometry is studied. Multiyear urban-rural temperature differences and building footprints data combined with a heat radiation scaling model are used to demonstrate for more than 50 cities worldwide that city texture-measured by a building distribution function and the sky view factor-explains city-to-city variations in nocturnal UHIs. Our results show a strong correlation between nocturnal UHIs and the city texture.

Figure

Figure

Figure

Figure

}, keywords = {IDEAL CONDITIONS; CLIMATE-CHANGE; CITIES; SIMULATION; GEOMETRY; ENERGY; HEALTH; IMPACT; MODEL}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.120.108701}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.120.108701}, author = {Sobstyl, Jake M. and Emig, Thorsten and Qomi, M. J. Abdolhosseini and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {611, title = {Surface temperatures in New York City: Geospatial data enables the accurate prediction of radiative heat transfer}, journal = {Scientific Reports}, volume = {8}, year = {2018}, month = {Feb-02-2018}, pages = { Article Number 2224 }, abstract = {

Despite decades of research seeking to derive the urban energy budget, the dynamics of thermal exchange in the densely constructed environment is not yet well understood. Using New York City as a study site, we present a novel hybrid experimental-computational approach for a better understanding of the radiative heat transfer in complex urban environments. The aim of this work is to contribute to the calculation of the urban energy budget, particularly the stored energy. We will focus our attention on surface thermal radiation. Improved understanding of urban thermodynamics incorporating the interaction of various bodies, particularly in high rise cities, will have implications on energy conservation at the building scale, and for human health and comfort at the urban scale. The platform presented is based on longwave hyperspectral imaging of nearly 100 blocks of Manhattan, in addition to a geospatial radiosity model that describes the collective radiative heat exchange between multiple buildings. Despite assumptions in surface emissivity and thermal conductivity of buildings walls, the close comparison of temperatures derived from measurements and computations is promising. Results imply that the presented geospatial thermodynamic model of urban structures can enable accurate and high resolution analysis of instantaneous urban surface temperatures.

}, keywords = {ENERGY-BALANCE; URBAN; STORAGE; MODEL; ALBEDO; FLUX}, doi = {10.1038/s41598-018-19846-5}, url = {http://www.nature.com/articles/s41598-018-19846-5}, author = {Ghandehari, Masoud and Emig, Thorsten and Aghamohamadnia, Milad} } @article {614, title = {Conformal field theory of critical Casimir forces between surfaces with alternating boundary conditions in two dimensions}, journal = {Journal of Statistical Mechanics: Theory and Experiment}, year = {2017}, month = {Mar-2017}, pages = { Article Number 033201 }, abstract = {

Systems as diverse as binary mixtures and inclusions in biological membranes, and many more, can be described effectively by interacting spins. When the critical fluctuations in these systems are constrained by boundary conditions, critical Casimir forces (CCF) emerge. Here we analyze CCF between boundaries with alternating boundary conditions in two dimensions, employing conformal field theory (CFT). After presenting the concept of boundary changing operators, we specifically consider two different boundary configurations for a strip of critical Ising spins: (I) alternating equi-sized domains of up and down spins on both sides of the strip, with a possible lateral shift, and (II) alternating domains of up and down spins of different size on one side and homogeneously fixed spins on the other side of the strip. Asymptotic results for the CCF at small and large distances are derived. We introduce a novel modified Szego formula for determinants of real antisymmetric block Toeplitz matrices to obtain the exact CCF and the corresponding scaling functions at all distances. We demonstrate the existence of a surface renormalization group flow between universal force amplitudes of different magnitude and sign. The Casimir force can vanish at a stable equilibrium position that can be controlled by parameters of the boundary conditions. Lateral Casimir forces assume a universal simple cosine form at large separations.

}, keywords = {Casimir effect; conformal field theory; critical exponents and amplitudes}, doi = {10.1088/1742-5468/aa5a68}, url = {http://stacks.iop.org/1742-5468/2017/i=3/a=033201?key=crossref.e58e04fb8593248b573c53589bed0f1d}, author = {Dubail, Jerome and Santachiara, Raoul and Emig, Thorsten} } @article {615, title = {Many-body heat radiation and heat transfer in the presence of a nonabsorbing background medium}, journal = {Physical Review B}, volume = {95}, year = {2017}, month = {Feb-15-2017}, abstract = {

Heat radiation and near-field radiative heat transfer can be strongly manipulated by adjusting geometrical shapes, optical properties, or the relative positions of the objects involved. Typically, these objects are considered as embedded in vacuum. By applying the methods of fluctuational electrodynamics, we derive general closed-form expressions for heat radiation and heat transfer in a system of N arbitrary objects embedded in a passive nonabsorbing background medium. Taking into account the principle of reciprocity, we explicitly prove the symmetry and positivity of transfer in any such system. Regarding applications, we find that the heat radiation of a sphere as well as the heat transfer between two parallel plates is strongly enhanced by the presence of a background medium. Regarding near- and far-field transfer through a gas like air, we show that a microscopic model (based on gas particles) and a macroscopic model (using a dielectric contrast) yield identical results. We also compare the radiative transfer through a medium like air and the energy transfer found from kinetic gas theory.

}, issn = {2469-9950}, doi = {10.1103/PhysRevB.95.085413}, url = {https://link.aps.org/doi/10.1103/PhysRevB.95.085413}, author = {M{\"u}ller, Boris and Incardone, Roberta and Antezza, Mauro and Emig, Thorsten and Kr{\"u}ger, Matthias} } @article {616, title = {Mechanisms of jamming in the Nagel-Schreckenberg model for traffic flow}, journal = {Physical Review E}, volume = {95}, year = {2017}, month = {Jan-2017}, abstract = {

We study the Nagel-Schreckenberg cellular automata model for traffic flow by both simulations and analytical techniques. To better understand the nature of the jamming transition, we analyze the fraction of stopped cars P(v=0) as a function of the mean car density. We present a simple argument that yields an estimate for the free density where jamming occurs, and show satisfying agreement with simulation results. We demonstrate that the fraction of jammed cars P(v\∈{0,1}) can be decomposed into the three factors (jamming rate, jam lifetime, and jam size) for which we derive, from random walk arguments, exponents that control their scaling close to the critical density.

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.95.012311}, url = {https://link.aps.org/doi/10.1103/PhysRevE.95.012311}, author = {Bette, Henrik M. and Habel, Lars and Emig, Thorsten and Schreckenberg, Michael} } @article {587, title = {Methodology for Estimation of Nanoscale Hardness via Atomistic Simulations}, journal = {Journal of Nanomechanics and Micromechanics}, volume = {7}, year = {2017}, month = {Dec-2017}, pages = { Article Number: UNSP 04017011 }, abstract = {

Statistical mechanics has provided powerful techniques to measure mechanical properties of materials at the nanoscale and paved the way for bottom-up computational materials design. The introduction of such techniques in civil engineering applications, namely construction and geotechnical materials, remains limited to the elastic and fracture properties. This paper presents an atomistic approach to calculate the nanoscale cohesion, friction angle, and hardness. This method is based on the application of biaxial external deformation, or stress, in the weakest crystallographic direction in the material. The onset of the failure is characterized by investigating the unloading paths from several points on the stress-strain curve. Such calculations of the failure stress along different deformation paths provide multiple failure Mohr circles in the normal-shear stress space, which is found to provide a failure envelope akin to the Mohr-Coulomb failure criterion that is widely used for the plastic analysis of granular geomaterials. The failure envelope characterizes the nanoscale cohesion and friction angle, which in conjunction with continuum mechanics can be utilized to estimate the nanoscale hardness of layered materials. Application of this method to tobermorite and Na-montmorillonite crystals yields values that are close to the experimental measurements obtained using nanoindentation and atomic force microscopy techniques. (C) 2017 American Society of Civil Engineers.

}, keywords = {Atomistic simulation; Friction; Cohesion; Hardness; Tobermorite; Montmorillonite}, issn = {2153-5434}, doi = {10.1061/(ASCE)NM.2153-5477.0000127}, url = {http://ascelibrary.org/doi/10.1061/\%28ASCE\%29NM.2153-5477.0000127}, author = {Qomi, M. J. Abdolhosseini and Ebrahimi, Davoud and Mathieu Bauchy and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {617, title = {Nonequilibrium Fluctuational Quantum Electrodynamics: Heat Radiation, Heat Transfer, and Force}, journal = {Annual Review of Condensed Matter Physics}, volume = {8}, year = {2017}, month = {Jan-11-2017}, pages = {119 - 143}, abstract = {

Quantum-thermal fluctuations of electromagnetic waves are the cornerstone of quantum statistics and inherent to phenomena such as thermal radiation and van der Waals forces. Although the principles are found in elementary texts, recent experimental and technological advances make it necessary to come to terms with counterintuitive consequences at short scales\—the so-called near-field regime. We focus on three manifestations: (a) The Stefan\–Boltzmann law describes radiation from macroscopic bodies but fails for small objects. (b) The heat transfer between two bodies at close proximity is dominated by evanescent waves and can be orders of magnitude larger than the classical (propagating) contribution. (c) Casimir forces, dominant at submicron separation, are not sufficiently explored for objects at different temperatures (at least experimentally). We explore these phenomena using fluctuational quantum electrodynamics (QED), introduced by Rytov in the 1950s, combined with scattering formalisms. This enables investigation of different material properties, shapes, separations, and arrangements.

}, issn = {1947-5454}, doi = {10.1146/annurev-conmatphys-031016-025203}, url = {http://www.annualreviews.org/doi/10.1146/annurev-conmatphys-031016-025203}, author = {Bimonte, Giuseppe and Emig, Thorsten and Kardar, Mehran and Kr{\"u}ger, Matthias} } @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 {612, title = {Temperature distribution and heat radiation of patterned surfaces at short wavelengths}, journal = {Physical Review E}, volume = {95}, year = {2017}, month = {May-03-2017}, pages = { Article Number 052104 }, abstract = {

We analyze the equilibrium spatial distribution of surface temperatures of patterned surfaces. The surface is exposed to a constant external heat flux and has a fixed internal temperature that is coupled to the outside heat fluxes by finite heat conductivity across the surface. It is assumed that the temperatures are sufficiently high so that the thermal wavelength (a few microns at room temperature) is short compared to all geometric length scales of the surface patterns. Hence the radiosity method can be employed. A recursive multiple scattering method is developed that enables rapid convergence to equilibrium temperatures. While the temperature distributions show distinct dependence on the detailed surface shapes (cuboids and cylinder are studied), we demonstrate robust universal relations between the mean and the standard deviation of the temperature distributions and quantities that characterize overall geometric features of the surface shape.

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.95.052104}, url = {http://link.aps.org/doi/10.1103/PhysRevE.95.052104}, author = {Emig, Thorsten} } @proceedings {338, title = {Contribution of mechanical factors to the variability of root architecture: Quantifying the past history of interaction forces between growing roots and soil grains}, journal = {2016 IEEE INTERNATIONAL CONFERENCE ON FUNCTIONAL-STRUCTURAL PLANT GROWTH MODELING, SIMULATION, VISUALIZATION AND APPLICATIONS (FSPMA)}, year = {2016}, month = {Nov-11-2016}, pages = {52-60}, publisher = {I E E E}, address = {NOV 07-11, 2016, Qingdao, PEOPLES R CHINA }, abstract = {

The relation between a growing root and the soil movement has often been under-estimated. The present work aims to determine how grains in granular soils are reorganized by the action of growing roots, and in turn how the resulting forces acting on root tips modify their development. For this purpose, we have developed a 2D Discrete Element Model (DEM) able to compute a numerical growth of a single root inside a granular medium, taking into account the grain-grain and the root-grain contact forces during the growth. First in silico simulations were carried out in order to : 1-quantify the influence of the granular structure (grain diameter distribution and gaps) and root mechanical properties (root bending stiffness) on the evolution of reaction forces applied to a single root during its growth; 2-highlight \“group effects\”, e.g. how the reorganization of grains and their interaction forces due to a given growing root can affect the mechanical signal perceived by its near neighbours; 3-investigate how the presence of initial channels within the granular medium can effect the growth trajectory and minimize the resistance to penetration. All simulations were carried out assuming that root growth direction was only driven by external forces. Simlation results allowed the extraction of general physical laws that will be used further to provide mechanoperceptive indicators and analyze experimental data provided by phenotyping platforms. The final objective will be to quantify the response of plants to mechanical stresses in terms of root elongation rate, root straightness and ramification.

}, doi = {10.1109/FSPMA.2016.7818288}, author = {Fakih, Mahmoud and Jean-Yves Delenne and Farhang Radja{\"\i} and Fourcaud, Thierry} } @article {250, title = {Effect of Polydispersity of Clay Platelets on the Aggregation And Mechanical Properties of Clay at the Mesoscale}, journal = {Clays and Clay Minerals}, volume = {64}, year = {2016}, month = {Aug-2016}, pages = {425 - 437}, abstract = {

The results from mesoscale simulations of the formation and evolution of microstructure for assemblies of Na-smectite particles based on assumed size distributions of individual clay platelets are presented here. The analyses predicted particle arrangements and aggregation (i.e. platelets linked in face-face configurations) and are used to link geometric properties of the microstructure and mechanical properties of the particle assemblies. Interactions between individual ellipsoidal clay platelets are represented using the Gay-Berne potential based on atomistic simulations of the free energy between two Na-smectite clay-platelets in liquid water, following a novel coarse-graining method developed previously. The current study describes the geometric (aggregate thickness, orientation, and porosity) and elastic properties in the \‘jammed states\’ from the mesoscale simulations for selected ranges of clay particle sizes and confining pressures. The thickness of clay aggregates for monodisperse assemblies increases (with average stack thickness consisting of n = 3-8 platelets) with the diameter of the individual clay platelets and with the level of confining pressure. Aggregates break down at high confining pressures (50-300 atm) due to slippage between the platelets. Polydisperse simulations generate smaller aggregates (n = 2) and show much smaller effects of confining pressure. All assemblies show increased order with confining pressure, implying more anisotropic microstructure. The mesoscale simulations are also in good agreement with macroscopic compression behavior measured in conventional 1-D laboratory compression tests. The mesoscale assemblies exhibit cubic symmetry in elastic properties. The results for larger platelets (D = 1000 \Å) are in good agreement with Nano-indentation measurements on natural clays and shale samples.

}, issn = {0009-8604}, doi = {10.1346/CCMN.2016.0640407}, author = {Ebrahimi, Davoud and Andrew J. Whittle and Roland Jean-Marc Pellenq} } @article {618, title = {Electromagnetic Casimir energy of a disk opposite a plane}, journal = {Physical Review A}, volume = {94}, year = {2016}, month = {Sep-15-2016}, abstract = {

Building on work by J. Meixner [Z. Naturforschung 3a, 506 (1948)], we show how to compute the exact scattering amplitude (or T-matrix) for electromagnetic scattering from a perfectly conducting disk. This calculation is a rare example of a nondiagonal T-matrix that can nonetheless be obtained in a semianalytic form. We then use this result to compute the electromagnetic Casimir interaction energy for a disk opposite a plane, for arbitrary orientation angle of the disk, for separations greater than the disk radius. We find that the proximity force approximation (PFA) significantly overestimates the Casimir energy, in the case of both the ordinary PFA, which applies when the disk is parallel to the plane, and the \“edge PFA\”, which applies when the disk is perpendicular to the plane.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.94.032509}, url = {https://link.aps.org/doi/10.1103/PhysRevA.94.032509}, author = {Emig, Thorsten and Graham, Noah} } @article {619, title = {Spectroscopic probe of the van der Waals interaction between polar molecules and a curved surface}, journal = {Physical Review A}, volume = {94}, year = {2016}, month = {Aug-17-2016}, abstract = {

We study the shift of rotational levels of a diatomic polar molecule due to its van der Waals interaction with a gently curved dielectric surface at temperature T, and submicron separations. The molecule is assumed to be in its electronic and vibrational ground state, and the rotational degrees are described by a rigid rotor model. We show that under these conditions retardation effects and surface dispersion can be neglected. The level shifts are found to be independent of T, and given by the quantum state averaged classical electrostatic interaction of the dipole with its image on the surface. We use a derivative expansion for the static Green\&$\#$39;s function to express the shifts in terms of surface curvature. We argue that the curvature induced line splitting is experimentally observable, and not obscured by natural linewidths and thermal broadening.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.94.022509}, url = {https://link.aps.org/doi/10.1103/PhysRevA.94.022509}, author = {Bimonte, Giuseppe and Emig, Thorsten and Jaffe, R. L. and Kardar, Mehran} } @article {326, title = {Velocity statistics of the Nagel-Schreckenberg model}, journal = {Physical Review E}, volume = {93}, year = {2016}, month = {Feb-18-2016}, pages = {Article Number: 022305}, abstract = {

The statistics of velocities in the cellular automaton model of Nagel and Schreckenberg for traffic are studied. From numerical simulations, we obtain the probability distribution function (PDF) for vehicle velocities and the velocity-velocity (vv) correlation function. We identify the probability to find a standing vehicle as a potential order parameter that signals nicely the transition between free congested flow for sufficiently large number of velocity states. Our results for the vv correlation function resemble features of a second order phase transition. We develop a 3-body approximation that allows us to relate the PDFs for velocities and headways. Using this relation, an approximation to the velocity PDF is obtained from the headway PDF observed in simulations. We find a remarkable agreement between this approximation and the velocity PDF obtained from simulations.

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.93.022305}, author = {Bain, Nicolas and Emig, Thorsten and Franz-Josef Ulm and Schreckenberg, Michael} } @article {179, title = {Advances in design and modeling of porous materials}, journal = {The European Physical Journal Special Topics}, volume = {224}, year = {2015}, month = {Jul-2015}, pages = {1653 - 1653}, abstract = {

This special issue of the European Physical Journal Special Topics is dedicated to selected papers from the symposium \“High surface area porous and granular materials\” organized in the frame of the conference \“Mat\ériaux 2014\”, held on November 24\–28, 2014 in Montpellier, France.

Porous materials and granular materials gather a wide variety of heterogeneous, isotropic or anisotropic media made of inorganic, organic or hybrid solid skeletons, with open or closed porosity, and pore sizes ranging from the centimeter scale to the sub-nanometer scale. Their technological and industrial applications cover numerous areas from building and civil engineering to microelectronics, including also metallurgy, chemistry, health, waste water and gas effluent treatment. Many emerging processes related to environmental protection and sustainable development also rely on this class of materials. Their functional properties are related to specific transfer mechanisms (matter, heat, radiation, electrical charge), to pore surface chemistry (exchange, adsorption, heterogeneous catalysis) and to retention inside confined volumes (storage, separation, exchange, controlled release). The development of innovative synthesis, shaping, characterization and modeling approaches enables the design of advanced materials with enhanced functional performance. The papers collected in this special issue offer a good overview of the state-of-the-art and science of these complex media.

We would like to thank all the speakers and participants for their contribution to the success of the symposium. We also express our gratitude to the organization committee of \“Mat\´eriaux 2014\”. We finally thank the reviewers and the staff of the European Physical Journal Special Topics who made the publication of this special issue possible.

}, issn = {1951-6355}, doi = {10.1140/epjst/e2015-02487-6}, author = {Ayral, Andre and Calas-Etienne, Sylvie and Benoit A. Coasne and Deratani, Andr{\'e} and Evstratov, Alexis and Anne Galarneau and Grande, Daniel and Hureau, Matthieu and Jobic, Herv{\'e} and Morlay, Catherine and Parmentier, Julien and Prelot, B{\'e}n{\'e}dicte and Rossignol, Sylvie and Simon-Masseron, Ang{\'e}lique and Thibault-Starzyk, Fr{\'e}d{\'e}ric} } @article {158, title = {Casimir-Polder force between anisotropic nanoparticles and gently curved surfaces}, journal = {Physical Review D}, volume = {92}, year = {2015}, month = {Jul-17-2015}, abstract = {

The Casimir--Polder interaction between an anisotropic particle and a surface is orientation dependent. We study novel orientational effects that arise due to curvature of the surface for distances much smaller than the radii of curvature by employing a derivative expansion. For nanoparticles we derive a general short distance expansion of the interaction potential in terms of their dipolar polarizabilities. Explicit results are presented for nano-spheroids made of SiO2 and gold, both at zero and at finite temperatures. The preferred orientation of the particle is strongly dependent on curvature, temperature, as well as material properties.

}, issn = {1550-7998}, doi = {10.1103/PhysRevD.92.025028}, author = {Bimonte, Giuseppe and Emig, Thorsten and Kardar, Mehran} } @proceedings {332, title = {Creep of Bulk C-S-H: Insights from Molecular Dynamics Simulations}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete StructuresCONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES }, year = {2015}, month = {Sep-17-2015}, pages = {511-516}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

Understanding the physical origin of creep in calcium\–silicate\–hydrate (C\–S\–H) is of primary importance, both for fundamental and practical interest. Here, we present a new method, based on molecular dynamics simulation, allowing us to simulate the long-term visco-elastic deformations of C\–S\–H. Under a given shear stress, C\–S\–H features a gradually increasing shear strain, which follows a logarithmic law. The computed creep modulus is found to be independent of the shear stress applied and is in excellent agreement with nanoindentation measurements, as extrapolated to zero porosity.

}, doi = {10.1061/978078447934610.1061/9780784479346.061}, author = {Mathieu Bauchy and Enrico Masoero and Franz-Josef Ulm and Roland Jean-Marc Pellenq}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @proceedings {333, title = {Creep of Clay: Numerical Results at the Scale of a Layer and Experimental Results at the Scale of Thin Self-Standing Films}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete StructuresCONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES }, year = {2015}, month = {Sep-17-2015}, pages = {531-536}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

This work focuses on the creep of clay-based materials, which exhibit significant analogies with cement-based materials. Here, we studied the creep of clay at two scales and with two techniques: numerically (with molecular simulations) at the scale of a clay layer (nm), and experimentally at the scale of thin self-standing clay films (few dozen m). At the scale of the clay layer, numerical simulations showed that the shear rate was constant over time and an affine function of the shear stress. Creep experiments showed that, after a transient period, the creep function of our thin self-standing clay films was a logarithmic function of time. A comparison of the results obtained at the two scales shows that the origin of the logarithmic feature of clay creep must at least partly originate from a scale greater than that of an individual clay layer. By analogy, such result is likely to hold for cementitious materials, which are also known to creep logarithmically with respect to time in the long term: the origin of this logarithmic feature is likely to stem at least partly from a scale greater than the scale of an individual C-S-H layer.

}, doi = {10.1061/978078447934610.1061/9780784479346.064}, author = {Benoit Carrier and Matthieu Vandamme and Roland Jean-Marc Pellenq and Henri Van Damme}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @article {157, title = {Critical Casimir force between inhomogeneous boundaries}, journal = {EPL (Europhysics Letters)}, volume = {112}, year = {2015}, month = {Dec-2015}, pages = {66004}, abstract = {

To study the critical Casimir force between chemically structured boundaries immersed in a binary mixture at its demixing transition, we consider a strip of Ising spins subject to alternating fixed spin boundary conditions. The system exhibits a boundary induced phase transition as function of the relative amount of up and down boundary spins. This transition is associated with a sign change of the asymptotic force and a diverging correlation length that sets the scale for the crossover between different universal force amplitudes. Using conformal field theory and a mapping to Majorana fermions, we obtain the universal scaling function of this crossover, and the force at short distances.

}, issn = {0295-5075}, doi = {10.1209/0295-5075/112/66004}, author = {Dubail, Jerome and Santachiara, Raoul and Emig, Thorsten} } @proceedings {331, title = {C-S-H across Length Scales: From Nano to Micron}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete StructuresCONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES }, year = {2015}, month = {Sep-17-2015}, pages = {39-48}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

Despite their impact on longevity, serviceability, and environmental footprint of our built infrastructure, the chemo-physical origins of nanoscale properties of cementitious materials, and their link to macroscale properties still remain rather obscure. Here, we discuss a multi-scale approach that describes different aspects of physical properties of C-S-H at the nano- and meso-scales. These include dynamics of water, thermal properties and mechanical behavior of C-S-H and its effect on properties of cement paste at different scales.

}, doi = {10.1061/978078447934610.1061/9780784479346.006}, url = {http://ascelibrary.org/doi/book/10.1061/9780784479346http://ascelibrary.org/doi/pdf/10.1061/9780784479346http://ascelibrary.org/doi/10.1061/9780784479346.006http://ascelibrary.org/doi/pdf/10.1061/9780784479346.006}, author = {Mohammad Javad Abdolhosseini Qomi and Enrico Masoero and Mathieu Bauchy and Franz-Josef Ulm and Emanuela Del Gado and Roland Jean-Marc Pellenq}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @article {161, title = {Effect of curvature and confinement on the Casimir-Polder interaction}, journal = {Physical Review A}, volume = {91}, year = {2015}, month = {Jan-30-2015}, abstract = {

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.

}, issn = {1050-2947}, doi = {10.1103/PhysRevA.91.012516}, author = {Rodriguez-Lopez, Pablo and Emig, Thorsten and Noruzifar, Ehsan and Zandi, Roya} } @proceedings {335, title = {Hydration Kinetics and Gel Morphology of C-S-H}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete StructuresCONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES}, year = {2015}, month = {Sep-17-2015}, pages = {565-573}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

Calcium-silicate hydrate (C-S-H) is the main binder in cement and concrete. It starts forming from the early stages of cement hydration and it progressively densifies as cement sets. C-S-H nanoscale building blocks form a cohesive gel, whose structure and mechanics are still poorly understood, in spite of its practical importance. Here we review a statistical physics approach recently developed, which allows us to investigate the C-S-H gel formation under the out-of-equilibrium conditions typical of cement hydration. Our approach is based on colloidal particles, precipitating in the pore solution and interacting with effective forces associated to the ionic environment. We present the evolution of the space filling of C-S-H with different particle interactions and compare them with experimental data at different lime concentrations. Moreover, we discuss the structural features of C-S-H in the mesoscale in terms of the scattering intensity. The comparison of our early stage C-S-H structures with small angle neutron scattering (SANS) experiments shows that long range spatial correlations and structural heterogeneties that develop in that early stages of hydration persist also in the hardened paste.

}, doi = {10.1061/978078447934610.1061/9780784479346.069}, author = {Katerina Ioannidou and Enrico Masoero and Pierre E. Levitz and Roland Jean-Marc Pellenq and Emanuela Del Gado}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @article {159, title = {Interplay of curvature and temperature in the Casimir{\textendash}Polder interaction}, journal = {Journal of Physics: Condensed Matter}, volume = {27}, year = {2015}, month = {Jun-03-2015}, pages = {214018}, abstract = {

We study the Casimir-Polder interaction at finite temperatures between a polarizable small, anisotropic particle and a non-planar surface using a derivative expansion. We obtain the leading and the next-to-leading curvature corrections to the interaction for low and high temperatures. Explicit results are provided for the retarded limit in the presence of a perfectly conducting surface.

}, issn = {0953-8984}, doi = {10.1088/0953-8984/27/21/214018}, author = {Bimonte, Giuseppe and Emig, Thorsten} } @proceedings {334, title = {Kinetic Simulations of Cement Creep: Mechanisms from Shear Deformations of Glasses}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete StructuresCONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES}, year = {2015}, month = {Sep-17-2015}, pages = {555-564}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

The logarithmic deviatoric creep of cement paste is a technical and scientific challenge. Transition State Theory (TST) indicates that some nanoscale mechanisms of shear deformation, associated with a specific kind of strain hardening, can explain the type of deviatoric creep observed experimentally in mature cement pastes. To test this possible explanation, we simulate the shear deformations of a colloidal model of cement hydrates at the nanoscale. Results from quasi-static simulations indicate a strain hardening analogous to that postulated by the TST approach. Additional results from oscillatory shear (fatigue) simulations show an increase of deformation with number of loading cycles that is consistent with the observed creep. These findings indicate that nanoscale simulations can improve our current understanding of the mechanisms underlying creep, with potential to go beyond the logarithmic creep and explore the onset of failure during tertiary creep.

}, doi = {10.1061/978078447934610.1061/9780784479346.068}, author = {Enrico Masoero and Mathieu Bauchy and Emanuela Del Gado and Hegoi Manzano and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Sidney Yip}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @proceedings {330, title = {The Meso-Scale Texture of Cement Hydrate Gels: Out-of-Equilibrium Evolution and Thermodynamic Driving}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete Structures CONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES}, year = {2015}, month = {Sep-17-2015}, pages = {34-38}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015 Vienna, AustriaReston, VA}, abstract = {

By the end of cement hydration calcium-silicate-hydrate (C-S-H) gels extends over tens and hundreds of nanometers. Their complex texture affects directly, and to a large extent, the macroscopic hygrothermal and mechanical behavior of cement. Here we review a statistical physics approach recently developed, which allows us to investigate the gel formation under the out-of-equilibrium conditions typical of cement hydration and the role of the nano-scale structure in C\—S\—H mechanics upon hardening. Our investigations have unveiled the role, in the C-S-H gels, of nano-scale structural and mechanical heterogeneities that develop due to the the far-from-equilibrium physico-chemical environment in which the material forms. A subtle interplay between the out-of-equilibrium evolution and the effective interactions emerging between the nano-scale units of the gels at different stages of the hydration process ultimately determines the mesoscale texture of cement hydrates and their material properties.

}, doi = {10.1061/978078447934610.1061/9780784479346.005}, author = {Emanuela Del Gado and Katerina Ioannidou and Enrico Masoero and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Sidney Yip}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @proceedings {358, title = {Micromechanical analysis of the surface erosion of a cohesive soil by means of a coupled LBM-DEM model}, journal = {IV International Conference on Particle-based Methods (PARTICLES 2015)}, volume = {PARTICLE-BASED METHODS IV-FUNDAMENTALS AND APPLICATIONS}, year = {2015}, month = {sept-30-2015}, pages = {519-528}, publisher = {International Center for Numerical Methods in Engineering (CIMNE)}, address = {SEP 28-30 2015 Barcelona, SPAIN}, abstract = {

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.

}, keywords = {Cohesion, DEM, LBM, Surface erosion}, url = {https://hal.archives-ouvertes.fr/hal-01269324}, author = {Cuellar, Pablo and Pierre Philippe and St{\'e}phane Bonelli and Benahmed, Nadia and Brunier-Coulin, Florian and Jeff Ngoma and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Onate, E and Bischoff, M and Owen, DRJ} } @proceedings {351, title = {Numerical simulation of granular media composed with irregular polyhedral particles: effect of particles{\textquoteright} angularity}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS}, year = {2015}, month = {Feb-02-2015}, pages = {222-228}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

We use contact dynamic simulations to perform a systematic investigation of the effects of particles shape angularity on mechanicals response in sheared granular ma-terials. The particles are irregular polyhedra with varying numbers of face from spheres to \"double pyramid\" shape with a constant aspect ratio. We study the quasi-static behav-ior, structural and force anisotropies of several packings subjected to triaxial compression. An interesting finding is that the shear strength first increases with angularity up to a maximum value and then saturates as the particles become more angular. Analyzing the anisotropies induced by the angular distributions of contacts and forces orientations, we show that the saturation of the shear strength at higher angularities is a consequence of fall-off of the texture anisotropies compensated by an increase of the tangential force anisotropy. This is attributed to the fact that at higher angularity, particles are bet-ter connected (or surrounded) leading to an increase of friction mobilization in order to achieve the deformation. Moreover, the most angular particles also have very few sides so that, this effect is enhanced by the increase of the proportion of face-side and side-side contacts with angularity.

}, keywords = {angularity, force transmission, Granular Materials, particle shape, texture}, url = {https://hal.archives-ouvertes.fr/hal-01112373}, author = {Emilien Az{\'e}ma and Farhang Radja{\"\i} and Dubois, Fr{\'e}d{\'e}ric}, editor = {Onate, E and Owen, DRJ} } @article {160, title = {Reversing the critical Casimir force by shape deformation}, journal = {Physics Letters B}, volume = {743}, year = {2015}, month = {Apr-09-2015}, pages = {138 - 142}, abstract = {

The exact critical Casimir force between periodically deformed boundaries of a 2D semi-infinite strip is obtained for conformally invariant classical systems. Only two parameters (conformal charge and scaling dimension of a boundary changing operator), along withthe solution of an electrostatic problem, determine the Casimir force, rendering the theory practically applicable to any shape and arrangement. The attraction between any two mirror symmetric objects follows directly from our general result. The possibility of purely shape induced reversal of the force, as well as occurrence of stable equilibrium points, is demonstrated for certain conformally invariant models, including the tricritical Ising model.

}, issn = {03702693}, doi = {10.1016/j.physletb.2015.02.038}, author = {Bimonte, Giuseppe and Emig, Thorsten and Kardar, Mehran} } @proceedings {357, title = {Rheology and Micromechanical Analysis of Granular Media Composed of Platy Particles: A Step Toward the DEM Simulation of Clayey Soils}, journal = {15th Pan-American Conference on Soil Mechanics and Geotechnical Engineering (PCSMGE) / 8th South American Congress on Rock Mechanics (SCRM)}, volume = {FROM FUNDAMENTALS TO APPLICATIONS IN GEOTECHNICS }, year = {2015}, month = {2015}, pages = {1357-1364}, address = {NOV 15-18 2015 Buenos Aires, ARGENTINA}, abstract = {

This work was carried out in the framework of a larger project devoted
to the micro-mechanical modeling of clayey soils by means of discrete element
simulations. Here, we study the rheology and microstructure of granular media
composed of platy particles. The particles are three-dimensional square plates,
approximated as spheropolyhedra. Several samples composed of particles of
different levels of platyness (related to the ratio of length to thickness) were
numerically prepared and sheared up to large deformations. Specifically, we
revisit and analyze in detail an ordering phenomenon described briefly in a
previous paper [1] and investigate its consequences in terms of the alignment of
particles and cluster formation. We find that particle alignment is strongly
enhanced by the degree of platyness and leads to the formation of face-connected
clusters. Due to dynamics, this spontaneous clustering is a robust characteristic of
granular systems composed of platy particles even in the absence of attraction
forces.

}, doi = {10.3233/978-1-61499-603-3-1357}, author = {Boton, Mauricio and Estrada, Nicolas and Emilien Az{\'e}ma}, editor = {Manzanal, D and Sfriso, AO} } @proceedings {329, title = {Shrinkage Due to Colloidal Force Interactions}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete Structures CONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES}, year = {2015}, month = {Sep-17-2015}, pages = {13-16}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA }, abstract = {

It has long been argued that shrinkage in cementitious materials can occur even in the absence of drying phenomena. Herein we argue that such shrinkage is attributable to colloidal forces that develop between C-S-H particles during the hydration in an out-of-equilibrium process. We base our argument on meso-scale simulation results, and show via microporomechanics theory that such colloidal forces can lead to the build-up of solid eigenstresses causing macroscopic shrinkage deformation.

}, doi = {10.1061/978078447934610.1061/9780784479346.002}, author = {Franz-Josef Ulm and Roland Jean-Marc Pellenq}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @proceedings {359, title = {Transient regime to fluidized chimney within a granular bed by means of a 2D DEM/LBM modeling}, journal = {IV International Conference on Particle-based Methods (PARTICLES 2015)}, volume = {PARTICLE-BASED METHODS IV-FUNDAMENTALS AND APPLICATIONS}, year = {2015}, month = {sept-30-2015}, pages = {558-566}, publisher = {International Center for Numerical Methods in Engineering (CIMNE)}, address = {SEP 28-30 2015 Barcelona, SPAIN}, abstract = {

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.

}, keywords = {DEM, Fluidization, Granular Materials, LBM}, url = {https://hal.archives-ouvertes.fr/hal-01269325}, author = {Jeff Ngoma and Pierre Philippe and St{\'e}phane Bonelli and Cuellar, Pablo and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Onate, E and Bischoff, M and Owen, DRJ} } @article {84, title = {Atomic-scale modelling of elastic and failure properties of clays}, journal = {Molecular Physics}, volume = {112}, year = {2014}, month = {May-19-2014}, pages = {1294-1305}, type = {Article}, abstract = {

The elastic and failure properties of a typical clay, illite, are investigated using molecular simulation. We employ a reactive (ReaxFF) and a non-reactive (ClayFF) force field to assess the elastic properties of the clay. As far as failure is concerned, ReaxFF was used throughout the study; however, some calculations were also performed with ClayFF. A crack parallel to the clay layers is found to have low fracture resistance when submitted to a tensile loading perpendicular to the crack. The mechanism of both yield and fracture failures is decohesion in the interlayer space. In contrast, under shear loading, the nanoscale failure mechanism is a stick-slip between clay layers. No fracture propagation is observed as the clay layers slide on top of each other. The low fracture resistance in mode I and the stick-slip failure in mode II are both the consequence of the lack of chemical bonds between clay layers where the cohesion is provided by non-covalent interactions. This work, which provides a description of the failure of clays at the microscopic scale, is the first step towards describing the failure of clays at a larger scale where the polycrystalline distribution of clay grains must be taken into account.

}, keywords = {clay, elastic properties, fracture, reactive molecular simulation}, issn = {0026-8976}, doi = {10.1080/00268976.2014.897393}, author = {Gy{\"o}rgy Hantal and Brochard, Laurent and Hadrien Laubie and Ebrahimi, Davoud and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Benoit A. Coasne} } @article {116, title = {Casimir-Polder interaction for gently curved surfaces}, journal = {Physical Review D}, volume = {90}, year = {2014}, month = {Oct-28-2014}, type = {Article}, abstract = {

We use a derivative expansion for gently curved surfaces to compute the leading and the next-to-leading curvature corrections to the Casimir-Polder interaction between a polarizable small particle and a nonplanar surface. While our methods apply to any homogeneous and isotropic surface, explicit results are presented here for perfect conductors. We show that the derivative expansion of the Casimir-Polder potential follows from a resummation of its perturbative series, for small in-plane momenta. We consider the retarded, nonretarded and classical high-temperature limits.

}, issn = {1550-7998}, doi = {10.1103/PhysRevD.90.081702}, author = {Bimonte, Giuseppe and Emig, Thorsten and Kardar, Mehran} } @article {113, title = {Mesoscale properties of clay aggregates from potential of mean force representation of interactions between nanoplatelets}, journal = {Journal of Chemical Physics }, volume = {140}, year = {2014}, month = {Apr-21-2014}, pages = {Article Number: 154309}, type = {Article}, abstract = {

Face-to-face and edge-to-edge free energy interactions of Wyoming Na-montmorillonite platelets were studied by calculating potential of mean force along their center to center reaction coordinate using explicit solvent (i.e., water) molecular dynamics and free energy perturbation methods. Using a series of configurations, the Gay-Berne potential was parametrized and used to examine the mesoscale aggregation and properties of platelets that are initially random oriented under isothermal-isobaric conditions. Aggregates of clay were defined by geometrical analysis of face-to-face proximity of platelets with size distribution described by a log-normal function. The isotropy of the microstructure was assessed by computing a scalar order parameter. The number of platelets per aggregate and anisotropy of the microstructure both increases with platelet plan area. The system becomes more ordered and aggregate size increases with increasing pressure until maximum ordered state at confining pressure of 50 atm. Further increase of pressure slides platelets relative to each other leading to smaller aggregate size. The results show aggregate size of (3-8) platelets for sodium-smectite in agreement with experiments (3-10). The geometrical arrangement of aggregates affects mechanical properties of the system. The elastic properties of the meso-scale aggregate assembly are reported and compared with nanoindentation experiments. It is found that the elastic properties at this scale are close to the cubic systems. The elastic stiffness and anisotropy of the assembly increases with the size of the platelets and the level of external pressure. (C) 2014 AIP Publishing LLC.

Image of FIG. 1.
Image of FIG. 2.
Image of FIG. 3.
Image of FIG. 4.
}, issn = {0021-9606}, doi = {10.1063/1.4870932}, author = {Ebrahimi, Davoud and Andrew J. Whittle and Roland Jean-Marc Pellenq} } @proceedings {251, title = {Mesoscale simulation of clay aggregate formation and mechanical properties}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro: Granular Matter}, year = {2014}, month = {Sep-2014}, pages = {539-544}, address = {SEP 01-03 2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

This paper proposes a novel methodology for understanding the meso-scale aggregation of clay platelets in water. We use Molecular Dynamics simulations using the CLAYFF force fields to represent the interactions between two layers of Wyoming montmorillonite (Na-smectite) in bulk water. The analyses are used to establish the potential of mean force at different spacings between the layers for edge-to-edge and face-to-face interactions. This is accomplished by finding the change in free energy as a function of the separation distance between the platelets using thermodynamic perturbation theory with a simple overlap sampling method. These nanoscale results are then used to calibrate the Gay\–Berne (GB) potential that represents each platelet as a single-site ellipsoidal body. A coarse-graining upscaling approach then uses the GB potentials and molecular dynamics to represent the meso-scale aggregation of clay platelets (at submicron length scale). Results from meso-scale simulations obtain the equilibrium/jamming configurations for mono-disperse clay platelets. The results show aggregation for a range of clay platelets dimensions and pressures with mean stack size ranging from 3 to 8 platelets. The particle assemblies become more ordered and exhibit more pronounced elastic anisotropy at higher confining pressures. The results are in good agreement with previously measured nano-indentation moduli over a wide range of clay packing densities.

}, issn = {1434-5021}, doi = {10.1007/s10035-016-0655-8}, author = {Ebrahimi, Davoud and Roland Jean-Marc Pellenq and Andrew J. Whittle}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin} } @article {272, title = {Particle alignment and clustering in sheared granular materials composed of platy particles}, journal = {The European Physical Journal E}, volume = {37}, year = {2014}, month = {Nov-24-2014}, pages = {Article Number: 116}, abstract = {

By means of molecular dynamics simulations, we investigate the texture and local ordering in sheared packings composed of cohesionless platy particles. The morphology of large packings of platy particles in quasistatic equilibrium is complex due to the combined effects of local nematic ordering of the particles and anisotropic orientations of contacts between particles. We find that particle alignment is strongly enhanced by the degree of platyness and leads to the formation of face-connected clusters of exponentially decaying size. Interestingly, due to dynamics in continuous shearing, this ordering phenomenon emerges even in systems composed of particles of very low platyness differing only slightly from spherical shape. The number of clusters is an increasing function of platyness. However, at high platyness the proportion of face-face interactions is too low to allow for their percolation throughout the system.

}, issn = {1292-8941}, doi = {10.1140/epje/i2014-14116-0}, author = {Boton, Mauricio and Estrada, Nicolas and Emilien Az{\'e}ma and Farhang Radja{\"\i}} } @proceedings {365, title = {AIP Conference Proceedings A multiscale description of failure in granular materials}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {585-588}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

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.

}, doi = {10.1063/1.4811999}, author = {Hadda, Nejib and Fran{\c c}ois Nicot and Sibille, Luc and Farhang Radja{\"\i} and Tordesillas, Antoinette and Darve, F{\'e}lix}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {366, title = {AIP Conference ProceedingsTumbling sandpiles in a fluid}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jul-2013}, pages = {662-665}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

By means of contact dynamics simulations interfaced with computational fluid dynamics, we analyze the effect of a suspending fluid on the dynamics of collapse and spread of a granular column. We find that the runout distance increases as a power law with the aspect ratio of the column and, for a given aspect ratio, it may be the same in the grain-inertial and fluid-inertial regimes but with considerably longer duration in the latter case. We show that, in both viscous and fluid-inertial regimes, this behavior results from compensation between two effects of the fluid: 1) reduction of the kinetic energy during collapse and 2) enhancement of the flow by lubrication during spread.

}, doi = {10.1063/1.4812018}, author = {Farhang Radja{\"\i} and Vincent Topin and Perales, F. and Yann Monerie}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {367, title = {A benchmark for particle shape dependence}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {883-886}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

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.

}, doi = {10.1063/1.4812073}, author = {Gael Combe and C{\'e}cile Nouguier-Lehon and Emilien Az{\'e}ma and Krzysztof Szarf and Baptiste Saint-Cyr and Marie Chaze and Farhang Radja{\"\i} and Pascal Villard and Jean-Yves Delenne and Vincent Richefeu and Philippe Sornay and Charles Voivret and CEGEO Group}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {369, title = {Capillary states of granular materials in the funicular state}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {1023-1026}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Using a multi-phase lattice Boltzmann model, we investigate the capillary states of a 2D granular packing gradually saturated by condensation from a homogeneously injected vapor phase. The internal stresses induced by surface tension and Laplace pressure are directly calculated from the forces acting on the grains with increasing amount of liquid. The evolution of cohesive strength with the amount of liquid reveals four different states reflecting the connectivity of the liquid phase and local grain environments. It increases in the pendular state, characterized by binary liquid bridges holding the grains together, and within the funicular state with an increasing number of liquid clusters connected to several grains. Beyond 40\% of saturation, the cohesive strength falls off due to a decreasing Laplace pressure of liquid clusters.

}, doi = {10.1063/1.4812108}, author = {Jean-Yves Delenne and Vincent Richefeu and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {368, title = {Comparison of the effects of rolling resistance and angularity in sheared granular media}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jul-2013}, pages = {891-894}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

In this paper, we compare the effect of rolling resistance at the contacts in granular systems composed of disks with the effect of angularity in granular systems composed of regular polygonal particles. For this purpose, we use contact dynamics simulations. By means of a simple shear numerical device, we investigate the mechanical behavior of these materials in the steady state in terms of shear strength, solid fraction, force and fabric anisotropies, and probability distribution of contact forces. We find that, based on the energy dissipation associated with relative rotation between two particles in contact, the effect of rolling resistance can explicitly be identified with that of the number of sides in a regular polygonal particle. This finding supports the use of rolling resistance as a shape parameter accounting for particle angularity and shows unambiguously that one of the main influencing factors behind the mechanical behavior of granular systems composed of noncircular particles is the partial hindrance of rotations as a result of angular particle shape.

}, keywords = {angularity, anisotropy, force distribution, Granular material, rolling resistance, Shear strength, solid fraction}, url = {https://hal.archives-ouvertes.fr/hal-00842799}, author = {Estrada, Nicolas and Emilien Az{\'e}ma and Farhang Radja{\"\i} and Taboada, Alfredo}, editor = {Yu, A and Dong, K and Yang, R} } @article {218, title = {Environmental scanning electron microscopy (ESEM) and nanoindentation investigation of the crack tip process zone in marble}, journal = {Acta Geotechnica}, volume = {8}, year = {2013}, month = {Jun-2013}, pages = {223 - 245}, abstract = {

This study explores the interaction between crack initiation and nanomechanical properties in the crack-tip fracture process zone of Carrara marble. Specimens with preexisting cracks were loaded in a uniaxial testing machine until the process zone appeared at the tips of the preexisting cracks. ESEM analysis reveals an increase in microcrack density in the process zone with increased loading of the specimen. Nanoindentation testing comprised of lines and grids of single nanoindentations located both near and far from the process zone shows a decrease in both indentation modulus and indentation hardness near grain boundaries in intact material, and with closeness to the process zone. Ultimately, the study confirms that the crack-tip process zone manifests itself as an area of reduced indentation hardness and indentation modulus in marble.

}, issn = {1861-1125}, doi = {10.1007/s11440-013-0213-z}, author = {Brooks, Z. and Franz-Josef Ulm and Einstein, H. H.} } @article {23, title = {Mesoscopic Monte Carlo simulations of microstructure and conductivity of zirconia-based ceramics}, journal = {J. Eur. Ceram. Soc.}, volume = {61}, year = {2013}, month = {Aug-2013}, pages = {5018-5025}, abstract = {

Zirconia-based refractories are ceramics that serve as furnaces for the production of high-quality speciality glasses. These materials are obtained by cooling a melt composed of different oxides and oxide precursors. The microstructure of these refractories consists of monoclinic zirconia embedded in a three-dimensional interconnected amorphous phase. Using mesoscopic Monte Carlo simulations, the present paper addresses the effect of the amount of amorphous phase and temperature on the microstructure of the material. The simulated microstructures resemble those obtained using tomography experiments. A theoretical model describing the electrical behavior of the material as a function of temperature and composition is also reported. In this model, the conductivity of the ZrO2 particles is assumed to be constant, but the overall conductivity of the sample depends on its tortuosity s. Comparison with experimental data suggests that the present model provides a realistic picture of the electrical behavior of zirconia-based ceramics and leads to quantitative predictions.

Image for unlabelled figure

}, doi = {10.1016/j.actamat.2013.04.044}, author = {P. Epicoco and Benoit A. Coasne and A. Gioia and P. Papet and I. Cabodi and M. Gaubil} } @proceedings {360, title = {Penetration strength of coarse granular materials from DEM simulations}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013 }, year = {2013}, month = {Jun-18-2013}, pages = { 241-244}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer test is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. In fact, the data are considerably more sensitive to various parameters such as fabric structure, particles shape or the applied impact energy. In order to achieve a better understanding of the underlying phenomena, we performed a numerical study by means contact dynamics DEM simulations. We consider the penetration of a moving tip into a sample composed of irregular grain shapes and we analyze the influence of the driving velocity and applied energy on the penetration strength. We find that the latter grows with both the penetration rate and energy. Force fluctuations on the tip involve a jamming-unjamming process. The typology of contact network and inter-granular friction play a major role in the fluctuations and measured values of the cone penetration strength.

}, doi = {10.1063/1.4811912}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @article {285, title = {Quasistatic rheology and microstructural description of sheared granular materials composed of platy particles}, journal = {Physical Review E}, volume = {87}, year = {2013}, month = {Mar-28-2013}, pages = {Article Number: 032206}, abstract = {

This is the first paper of a series devoted to the micro-mechanical modeling of clayey soils, by means of discrete element simulations. We specifically focus here on the effect of the platy shape of particles by reducing the interactions between particles to mechanical contact forces (i.e., neither electrostatic repulsion nor van der Waals forces are taken into account). The particles are three-dimensional square plates, approximated as spheropolyhedra. Several samples composed of particles of different levels of platyness (related to the ratio of length to thickness) were numerically prepared and sheared up to large deformations. We analyzed the shear strength, packing fraction, orientation of the particles, connectivity, fabric of the interactions network, and interaction forces as functions of the platyness. We find that both the mechanical behavior and microstructure are strongly dependent on the degree of platyness. The principal underlying phenomenon is the alignment of particle faces along a particular direction. This ordering phenomenon, which emerges even for shapes that deviate only slightly from that of a sphere, enhances the ability of the packing to develop an anisotropic structure leading to large shear strength, especially as a consequence of the fabric and mobilization of friction forces. Moreover, the connectivity of the packings and their packing fraction also evolve with the platyness. In particular, the packing fraction evolves in a nonmonotonic fashion, as observed in other granular materials composed of elongated or angular particles.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.87.032206}, author = {Boton, Mauricio and Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i} and Lizcano, Arcesio} } @proceedings {361, title = {Settlement statistics of a granular layer composed of polyhedral particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {333-336}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

We use 3D contact dynamics simulations to investigate the mechanical equilibrium and settlement of a granular material composed of irregular polyhedral particles confined between two horizontal frictional planes. We show that, as a consequence of mobilized wall-particle friction force at the top and bottom boundaries, the transient deformation induced by a constant vertical load increment is controlled by the aspect ratio (thickness over width) of the packing as well as the stress ratio. The transient deformation declines considerably for increasingly smaller aspect ratios and grows with the stress ratio. From the simulation data for a large number of independent configurations, we find that sample-to-sample fluctuations of the deformation have a broad distribution and they scale with the average deformation.

}, doi = {10.1063/1.4811935}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {363, title = {Shear strength and microstructure of 3D assemblies of platy particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jul-09-2013}, pages = {519-522}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

As a first step towards particle-scale modeling of clayey soils, we investigate the mechanical behavior and microstructure of assemblies of three-dimensional rectangular platy particles by means of the discrete element method. Several samples composed of particles of different levels of platyness (ratio of width to thickness) were numerically prepared and sheared to large deformations. We analyze the shear strength, packing fraction, connectivity, contact and force anisotropies, and mobilization of friction forces as functions of platyness.We find that both the mechanical behavior and microstructure are strongly dependent on the degree of platyness. This happens, in particular, because of the alignment of particle faces along a particular direction. Additionally, as observed for other granular materials with complex shapes, the packing fraction passes by a peak value before decreasing for larger values of platyness.

}, keywords = {Clays, DEM, Microstructure, Shear strength}, url = {https://hal.archives-ouvertes.fr/hal-00842787}, author = {Boton, Mauricio and Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i} and Lizcano, Arcesio}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {362, title = {Shear strength, force distributions and friction mobilization in sheared packings composed of angular particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {2013}, pages = {511-514}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

In this paper, we explore the effect of particle shape angularity on the mechanical behavior of sheared granular packings. A first series of contact dynamics simulations is performed in 2D with regular polygons with an increasing number of sides ranging from 3 (triangles) to 60. Then, in order to approach \“idealized\” angular particles, a second series of simulations is performed in 3D with irregular polyhedra with the number of faces ranging from 8 (octahedron-like) to 596. A counterintuitive finding is that the shear strength increases with angularity up to a maximum value and saturates as the particles become more angular (below 6 sides in 2D and 46 faces in 3D). A micromechanical analysis of force and contact orientations, all enhanced by face-face and face-side contacts, reveals that this increase is due to an increase of both contact and force anisotropies, and the saturation for higher angularities is a consequence of a rapid fall-off of the contact and normal force anisotropies compensated by an increase of the tangential force anisotropy.

}, doi = {10.1063/1.4811980}, author = {Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {350, title = {Effect of Particle Shape non-Convexity on the Rheology of Granular Media : 3D Contact Dynamics Simulations}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS}, year = {2012}, month = {Apr-10-2012}, pages = {427-434}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

We analyze the effect of particle shape non-convexity on the quasi-static behavior of granular materials by means of contact dynamics simulations. The particles are regular aggregates of four overlapping spheres described by a nonconvexity parameter depending on the relative positions of the particles. Several packings are first submitted to isotropic compression without friction. We find that, as in 2D, the solid fraction of isotropic packings increases with non-convexity up to a maximum value and then declines to be nearly equal to that of a packing composed of only spheres. It is also remarkable that the coordination number increases quickly and saturates so that the packings composed of grains with a high level of nonconvexity are looser but more strongly connected. Then, the quasi-static behavior, structural and force anisotropies are analyzed by subjecting each packing to a triaxial compression. We find that the shear strength increases with non-convexity. We show that this increase results from the presence of multiple contacts between trimers leading to enhanced frictional interlocking.

}, keywords = {force transmission, Granular Materials, non-convexity, particle shape, texture}, url = {https://hal.archives-ouvertes.fr/hal-00686453}, author = {Baptiste Saint-Cyr and Emilien Az{\'e}ma and Jean-Yves Delenne and Farhang Radja{\"\i} and Philippe Sornay}, editor = {Onate, E and Owen, DRJ} } @proceedings {354, title = {Microscopic Origins of Shear Strength in Packings Composed of Elongated Particles}, journal = {9th International Workshop on Bifurcation and Degradation in Geomaterials (IWBDG 2011)}, volume = {Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS}, year = {2012}, month = {Apr-11-2012}, pages = {21-27}, address = {MAY 23-26 2011 Porquerolles, FRANCE}, abstract = {

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.

}, keywords = {Elongated particles, Fabric properties, force transmission, Harmonic decomposition}, url = {https://hal.archives-ouvertes.fr/hal-00686728}, author = {Emilien Az{\'e}ma and Farhang Radja{\"\i}}, editor = {St{\'e}phane Bonelli and Dascalu, Cristian and Fran{\c c}ois Nicot} } @article {47, title = {Nanoscale Elastic Properties of Montmorillonite upon Water Adsorption}, journal = {Langmuir}, volume = {28}, year = {2012}, month = {Dec-11-2012}, pages = {16855{\textendash}16863}, abstract = {
Abstract Image

Smectites are an important group of clay minerals that experience swelling upon water adsorption. This paper uses molecular dynamics with the CLAYFF force field to simulate isothermal isobaric water adsorption of interlayer Wyoming Na-montmorillonite, a member of the smectite group. Nanoscale elastic properties of the clay\–interlayer water system are calculated from the potential energy of the model system. The transverse isotropic symmetry of the elastic constant matrix was assessed by calculating Euclidean and Riemannian distance metrics. Simulated elastic constants of the clay mineral are compared with available results from acoustic and nanoindentation measurements.

}, doi = {10.1021/la302997g}, author = {Ebrahimi, Davoud and Roland Jean-Marc Pellenq and Andrew J. Whittle} } @article {296, title = {Nonlinear effects of particle shape angularity in sheared granular media}, journal = {Physical Review E}, volume = {86}, year = {2012}, month = {Oct-01-2012}, pages = { Article Number: 041301 Part: 1}, abstract = {

We analyze the effects of particle shape angularity on the macroscopic shear behavior and texture of granular packings simulated by means of the contact dynamics method. The particles are regular polygons with an increasing number of sides ranging from 3 (triangles) to 60. The packings are analyzed in the steady shear state in terms of their shear strength, packing fraction, connectivity, and fabric and force anisotropies, as functions of the angularity. An interesting finding is that the shear strength increases with angularity up to a maximum value and saturates as the particles become more angular (below six sides). In contrast, the packing fraction declines towards a constant value, so that the packings of more angular particles are looser but have higher shear strength. We show that the increase of the shear strength at low angularity is due to an increase of both contact and force anisotropies, and the saturation of the shear strength for higher angularities is a consequence of a rapid fall-off of the contact and normal force anisotropies compensated by an increase of the tangential force anisotropy. This transition reflects clearly the rather special geometrical properties of these highly angular shapes, implying that the stability of the packing relies strongly on the side-side contacts and the mobilization of friction forces.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.86.041301}, author = {Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i}} } @proceedings {356, title = {Compressive strength of an unsaturated granular material during cementation}, journal = {Symposium on Science and Technology of Powders and Sintered Materials (STPMF 2009)}, volume = {POWDER TECHNOLOGY}, year = {2011}, month = {Mar-25-2011}, pages = {308 - 311}, address = {MAY 25-27 2009 Montpellier, FRANCE}, abstract = {

The cohesive behaviour of unsaturated granular materials is due to the presence of cohesive bonds between grains. These bonds can have various physico-chemical characteristics and may evolve with environmental conditions. We study the case of a granular material partially saturated by an aqueous solution. The bonds are thus initially of capillary type and the mechanical strength is weak. At low relative humidity, the phase change of water involves crystallization of the solute at the contact points between grains, generating thus solid bonds. The mechanical strength of the material is then enhanced. An experimental study of the evolution of the mechanical strength during crystallization of the solute shows clearly the transition from capillary regime to cemented regime. This transition is not correlated with the mass of the crystallized solute, but rather with the residual degree of saturation. This behavior is analyzed here in the light of discrete element simulations. We introduce a local cohesion law that accounts for transition from capillary to cemented bonding. This law is formulated in terms of the degree of crystallization as a result of the evaporation of water at the boundary of the sample. The cohesion of the packing is initially of capillary type. A crystallization front then spreads from the sample boundaries to the center of the sample, and the strength increases as a result. Uniaxial compression allows us to determine the strength at different times. The numerical strength agrees well with the experimental data, and reveals strength enhancement as the solute crystallizes, as well as the transition from capillary to cementation regime.

}, issn = {00325910}, doi = {10.1016/j.powtec.2010.08.021}, author = {Jean-Yves Delenne and Souli{\'e}, Fabien and Moulay Sa{\"\i}d El Youssoufi and Farhang Radja{\"\i}} } @proceedings {349, title = {Creep behaviour of confined layers of polyhedral grains}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS }, year = {2011}, month = {Oct-2011}, pages = {574-583}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

By means of contact dynamics simulations, we investigate the creep deformation of a thin granular layer composed of irregular polyhedral particles under the action of a constant vertical overload applied on a horizontal wall on top of the layer. We show that the total deformation induced by the overload increases with the ratio between the vertical and confining horizontal stresses and the aspect ratio of the sample. The effect of the aspect ratio is a consequence of the mobilized wall-grain friction forces at the top and bottom boundaries, that lead to enhanced strength by stabilizing strong force chains at the center of the sample. We also evidence the influence of loading history due to strain-induced fabric change or inertial effects resulting from the instant application of the overload. The topology of the contact network evolves in close correlation with creep. In particular, the face/face contacts between polyhedral particles concentrate largest force chains and their number is an increasing function of creep. A crucial feature of a confined granular system is the statistical variability of the mechanical response that we analyzed for creep deformations by performing a large number of simulations for independent initial configurations. Our data indicate that the distribution of fluctuations with respect to the mean creep falls off exponentially.

}, url = {https://hal.archives-ouvertes.fr/hal-00761094}, author = {Quezada, Juan Carlos and Farhang Radja{\"\i} and Breul, Pierre and Saussine, Gilles}, editor = {Onate, E and Owen, DRJ} } @article {316, title = {From liquid to solid bonding in cohesive granular media}, journal = {Mechanics of Materials}, volume = {43}, year = {2011}, month = {Oct-2011}, pages = {529 - 537}, abstract = {

We study the transition of a granular packing from liquid to solid bonding in the course of drying. The particles are initially wetted by a liquid brine and the cohesion of the packing is ensured by capillary forces, but the crystallization of the solute transforms the liquid bonds into partially cemented bonds. This transition is evidenced experimentally by measuring the compressive strength of the samples at regular intervals of times. Our experimental data reveal three regimes: (1) Up to a critical degree of saturation, no solid bonds are formed and the cohesion remains practically constant; (2) The onset of cementation occurs at the surface and a front spreads towards the center of the sample with a nonlinear increase of the cohesion; (3) All bonds are partially cemented when the cementation front reaches the center of the sample, but the cohesion increases rapidly due to the strengthening of cemented bonds. We introduce a model based on a parametric cohesion law at the bonds and a bond crystallization parameter. This model predicts correctly the phase transition and the relation between microscopic and macroscopic cohesion.

Fig. 1. (a) Photograph of the sample in the process of drying; (b) The press used for{\textellipsis}

Fig. 2. Compressive yield stress σY, normalized by the yield stress σLY due only to{\textellipsis}

Fig. 3. Photograph of a partially dried sample in the second regime

Fig. 4. Schematic representation of the evolution of bridge: from a liquid to a solid{\textellipsis}

Fig. 5. Evolution of the global crystallization index with time; solid line:{\textellipsis}

Fig. 6. The parametric adhesion law

}, issn = {01676636}, doi = {10.1016/j.mechmat.2011.06.008}, author = {Jean-Yves Delenne and Souli{\'e}, Fabien and Moulay Sa{\"\i}d El Youssoufi and Farhang Radja{\"\i}} } @article {317, title = {Identification of rolling resistance as a shape parameter in sheared granular media}, journal = {Physical Review E}, volume = {84}, year = {2011}, month = {Jul-28-2011}, pages = {Article Number: 011306 Part: 1}, abstract = {

Using contact dynamics simulations, we compare the effect of rolling resistance at the contacts in granular systems composed of disks with the effect of angularity in granular systems composed of regular polygonal particles. In simple shear conditions, we consider four aspects of the mechanical behavior of these systems in the steady state: shear strength, solid fraction, force and fabric anisotropies, and probability distribution of contact forces. Our main finding is that, based on the energy dissipation associated with relative rotation between two particles in contact, the effect of rolling resistance can explicitly be identified with that of the number of sides in a regular polygonal particle. This finding supports the use of rolling resistance as a shape parameter accounting for particle angularity and shows unambiguously that one of the main influencing factors behind the mechanical behavior of granular systems composed of noncircular particles is the partial hindrance of rotations as a result of angular particle shape.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.84.011306}, author = {Estrada, Nicolas and Emilien Az{\'e}ma and Farhang Radja{\"\i} and Taboada, Alfredo} } @proceedings {352, title = {Modeling Porous Granular Aggregates}, journal = {9th International Workshop on Buifurcation and Degradation in Geomaterials (IWBDG 2011)}, volume = {Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS}, year = {2011}, month = {May-28-2011}, pages = {249 - 254}, publisher = {Springer Netherlands}, address = {MAY 23-26 2011 Porquerolles, FRANCE}, abstract = {

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.

}, isbn = {978-94-007-1420-5}, issn = {1866-8755}, doi = {10.1007/978-94-007-1421-2_32}, author = {Rafik Aff{\`e}s and Vincent Topin and Jean-Yves Delenne and Yann Monerie}, editor = {St{\'e}phane Bonelli and Dascalu, Cristian and Fran{\c c}ois Nicot} } @proceedings {353, title = {Onset of Immersed Granular Avalanches by DEM-LBM Approach}, journal = {9th International Workshop on Buifurcation and Degradation in Geomaterials (IWBDG 2011)}, volume = {Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS}, year = {2011}, month = {May-28-2011}, pages = {109 - 115}, publisher = {Springer Netherlands}, address = {MAY 23-26 2011 Porquerolles, FRANCE}, abstract = {

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.

}, isbn = {978-94-007-1420-5}, issn = {1866-8755}, doi = {10.1007/978-94-007-1421-210.1007/978-94-007-1421-2_14}, author = {Jean-Yves Delenne and Mansouri, M. and Farhang Radja{\"\i} and Moulay Sa{\"\i}d El Youssoufi and Seridi, A.}, editor = {St{\'e}phane Bonelli and Dascalu, Cristian and Fran{\c c}ois Nicot} } @proceedings {364, title = {Springer Series in Geomechanics and Geoengineering Multiscale and Multiphysics Processes in Geomechanics SIMULATION OF HYDRATION AND ELASTIC PROPERTIES OF MONTMORILLONITE USING MOLECULAR DYNAMICS}, journal = {International Workshop on Multiscale and Multiphysics Processes in Geomechanics}, volume = {Springer Series in Geomechanics and Geoengineering}, year = {2011}, month = {2011}, pages = {105 - 108}, publisher = {Springer Berlin Heidelberg}, address = {JUN 23-25 2010 Stanford Univ, Stanford, CA}, abstract = {

This article describes molecular-level simulations of the adsorption isotherm and elastic properties for a Wyoming Na-montmorillonite using the General Utility Lattice Program. The selected clay mineral includes isomorphous substitutions in both the silica tetrahedral and octahedral gibbsite sheets. The resulting negative charges are balanced by Na+ cations. The authors have investigated the importance of different interatomic potentials in understanding the adsorption of water molecules (at ambient temperature, 300K). A unique combination of NPT and Grand Canonical ensemble simulations using Core\–Shell potential shows intra-layer adsorption, while the same approach based on empirical CLAYFF potential produces only interlayer water adsorption. There is a correspondingly large difference in the theoretical elastic modulus normal to the clay sheets using the two different sets of force potentials. This article discusses the underlying reasons for these differences and reviews the experimental evidence supporting intra-layer water absorption in montmorillonite.

}, isbn = {978-3-642-19629-4}, issn = {1866-8755}, doi = {10.1007/978-3-642-19630-0_27}, author = {Roland Jean-Marc Pellenq and Andrew J. Whittle and Ebrahimi, Davoud}, editor = {Borja, Ronaldo I. and Wu, Wei} }