This paper discusses the notion of failure in a granular assembly by examining the key microstructural mechanisms which are most likely to trigger the nucleation and propagation of instabilities within a granular material. For this purpose, the key variable to predict the occurrence of failure, known as second-order work, is expressed from variables on the grain scale. The local behaviour incidents (where contacts may open or slide), compared to the global response of the assembly, are analysed by two approaches. First, numerical computations made by a discrete element model confirm the microscopic definition of the second-order work. Secondly, a micromechanical model, based on a homogenization procedure, relating the macroscopic behaviour to microscopic ingredients, namely contact planes, points to a close link between the occurrence of failure on the macroscopic scale as well as on the contact planes.

VL - 342 IS - 3 JO - Comptes Rendus Mécanique ER - TY - Generic T1 - AIP Conference Proceedings A multiscale description of failure in granular materials T2 - 7th International Conference on Micromechanics of Granular Media (Powders and Grains) Y1 - 2013 A1 - Hadda, Nejib A1 - François Nicot A1 - Sibille, Luc A1 - Farhang Radjaï A1 - Tordesillas, Antoinette A1 - Darve, Félix ED - Yu, A ED - Dong, K ED - Yang, R AB -This paper presents conditions of initiation and development of failure in granular materials through a twodimensional discrete element model. General condition for the effective development of failure and its physical characteristics are recalled. Then relation between failure and the second order work expressed in terms of microscopic variables is discussed. Eventually, correspondence between a localized mode of failure marked with shear band patterns and space distribution of negative values of microscopic second-order work is investigated.

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

We investigate the rheology, force transmission and texture of granular materials composed of elongated particles by means of contact dynamics simulations. The particles have a rounded-cap rectangular (RCR) shape described by a single elongation parameter varying from 0 for a circular particle to 1 for an infinitely thin or long particle. We study the quasi-static behavior, structural and force anisotropies as a function of the elongation parameter for packings submitted to biaxial compression. The shear strength is found to increase linearly with this parameter whereas the solid fraction both at the initial isotropic state and in the critical state is nonmonotonous. We show that for these elongated particles a harmonic decomposition of the stress tensor provides a fairly good approximation of the internal state. Our data suggest that the increase of shear strength with reflects both enhanced friction mobilization and anisotropic particle orientation as the elongation of the particles increases.

JF - 9th International Workshop on Bifurcation and Degradation in Geomaterials (IWBDG 2011) CY - MAY 23-26 2011 Porquerolles, FRANCE VL - Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS UR - https://hal.archives-ouvertes.fr/hal-00686728 ER - TY - Generic T1 - Modeling Porous Granular Aggregates T2 - 9th International Workshop on Buifurcation and Degradation in Geomaterials (IWBDG 2011) Y1 - 2011 A1 - Rafik Affès A1 - Vincent Topin A1 - Jean-Yves Delenne A1 - Yann Monerie ED - Stéphane Bonelli ED - Dascalu, Cristian ED - François Nicot AB -We rely on 3D simulations based on the Lattice Element Method (LEM) to analyze the failure of porous granular aggregates under tensile loading. We investigate crack growth by considering the number of broken bonds in the particle phase as a function of the matrix volume fraction and particle-matrix adhesion. Three regimes are evidenced, corresponding to no particle damage, particle abrasion and particle fragmentation, respectively. We also show that the probability density of strong stresses falls off exponentially at high particle volume fractions where a percolating network of jammed particles occurs. Decreasing the matrix volume fraction leads to increasingly broader stress distribution and hence a higher stress concentration. Our findings are in agreement with 2D results previously reported in the literature.

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

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