@article {628, title = {Inertial shear flow of assemblies of frictionless polygons: Rheology and microstructure}, journal = {The European Physical Journal E}, volume = {4}, year = {2018}, month = {Jan-05-2018}, pages = { Article Number 2 }, abstract = {

Motivated by the understanding of shape effects in granular materials, we numerically investigate the macroscopic and microstructural properties of anisotropic dense assemblies of frictionless polydisperse rigid pentagons in shear flow, and compare them with similar systems of disks. Once subjected to large cumulative shear strains their rheology and microstructure are investigated in uniform steady states, depending on inertial number I, which ranges from the quasistatic limit (I similar to 10(-5)) to 0.2. In the quasistatic limit both systems are devoid of Reynolds dilatancy, i.e., flow at their random close packing density. Both macroscopic friction angle., an increasing function of I, and solid fraction., a decreasing function of I, are larger with pentagons than with disks at small I, but the differences decline for larger I and, remarkably, nearly vanish for I similar to 0.2. Under growing I, the depletion of contact networks is considerably slower with pentagons, in which increasingly anisotropic, but still well-connected force-transmitting structures are maintained throughout the studied range. Whereas contact anisotropy and force anisotropy contribute nearly equally to the shear strength in disk assemblies, the latter effect dominates with pentagons at small I, while the former takes over for I of the order of 10(-2). The size of clusters of grains in side-to-side contact, typically comprising more than 10 pentagons in the quasistatic limit, very gradually decreases for growing I.

}, keywords = {CONTACT DYNAMICS METHOD; DENSE GRANULAR FLOWS; GEOMETRIC ORIGIN; BEHAVIOR; PACKING; MEDIA; SHAPE}, issn = {1292-8941}, doi = {10.1140/epje/i2018-11608-9}, url = {http://link.springer.com/10.1140/epje/i2018-11608-9}, author = {Emilien Az{\'e}ma and Farhang Radja{\"\i} and Jean-Noel~ Roux} } @article {264, title = {Modeling Granular Materials: Century-Long Research across Scales}, journal = {Journal of Engineering Mechanics}, volume = {143}, year = {2017}, month = {Jan-23-2017}, pages = {Article Number: UNSP 04017002}, abstract = {

Granular materials are the most recurrent form of solid-state matter on Earth. They challenge researchers and engineers in various fields not only because they occur with a broad variety of grain sizes, shapes and interactions in nature and industry, but also because they show a rich panoply of mechanical states. Despite this polymorphism, all these different types of soils, powders, granules, ores, pharmaceutical products, etc., are instances of the granular matter with the same least common denominator of being sandlike (psammoid in Greek), i.e.,\ solid grains interacting via frictional contacts. This review describes milestone contributions to the field of granular materials since the early elastic-plastic models developed for soils in the 1950s. The research on granular materials has grown into a vast multidisciplinary field in the 1980s with increasing focus on the microstructure and owing to new experimental tools and discrete simulation methods. It turns out that the granular texture, particle-scale kinematics, and force transmission are far more complex than presumed in early micromechanical models of granular materials. Hence, constitutive relations cannot easily be derived from the particle-scale behavior although advanced continuum models have been developed to account for anisotropy, intermediate stress, and complex loading paths. The subtle elastic properties and origins of bulk friction will be discussed, as well as the effects of particle shape and size distributions. The review covers also recent developments in macroscopic modeling such as the thermomechanical approach, anisotropic critical state theory, nonlocal modeling approach, inertial flows, and material instabilities. Finally, a brief account is given of open issues and some new frontiers and challenges in the field.

}, issn = {0733-9399}, doi = {10.1061/(ASCE)EM.1943-7889.0001196}, author = {Farhang Radja{\"\i} and Jean-Noel~ Roux and Daouadji, Ali} } @article {154, title = {Internal friction and absence of dilatancy of packings of frictionless polygons}, journal = {Physical Review E}, volume = {91}, year = {2015}, month = {Jan-30-2015}, pages = {Article Number: 010202}, abstract = {

By means of numerical simulations, we show that assemblies of frictionless rigid pentagons in slow shear flow possess an internal friction coefficient (equalto0.183\±0.008 with our choice of moderately polydisperse grains) but no macroscopic dilatancy. In other words, despite side-side contacts tending to hinder relative particle rotations, the solidfraction under quasistatic shear coincides with that of isotropic random close packings of pentagonal particles. Properties of polygonal grains are thus similar to those of disks in that respect. We argue that continuous reshuffling of the force-bearing network leads to frequent collapsing events at the microscale, thereby causing the macroscopic dilatancy to vanish. Despite such rearrangements, the shear flow favors an anisotropic structure that is at the origin of the ability of the system to sustain shear stress.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.91.010202}, author = {Emilien Az{\'e}ma and Farhang Radja{\"\i} and Jean-Noel~ Roux} }