Finite element analysis of localization and micro–macro structure relation in granular materials. Part I: Formulation (original) (raw)
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Formación de bandas de corte en materiales granulares: una aproximación micromecánica
Epsilon, 2009
Shear bands as mode of failure in granular soils has been largely studied without to physically explain the formation mechanism of that, neither to reproduce exactly a defined failure pattern. Several algorithms were performed with a distinct element method. In this ones, are looking for to reproduce only shear band in a biaxial simulation on rigid disk assembly, to get information at shear zone.
Shear band formation in granular materials: a micromechanical approach
abstract Shear bands as mode of failure in granular soils has been largely studied without to physically explain the formation mechanism of that, neither to reproduce exactly a defined failure pattern. Several algorithms were performed with a distinct element method. In this ones, are looking for to reproduce only shear band in a biaxial simulation on rigid disk assembly, to get information at shear zone.
Taylor & Francis eBooks, 2003
The mechanical behaviour of a frictional granular material is strongly influenced by both fabric (anisotropy of grain packing) and grain contact force networks that develop during plastic deformations. When a sand body is sheared, an increase in volume (dilation) ensues as a consequence of geometrical constraints imposed by the fabric against applied stresses. This important phenomenon coined as stress-dilatancy hinges on particle kinematics (slip and spin) as the grains override each other against confinement. As such, both dilatancy and fabric control the nature of the deformation mode, e.g. the localization of deformations into a shear band, which usually signals incipient failure. It has been found that the dominant mechanism inside a shear band is that of particle rearrangement, including both rolling and translation leading into further fabric changes with respect to the region outside the shear band. In fact, Oda et al. (1998) and Desrues et al. (1996) both observed significant particle rotation and increase of voids within the shear band. Therefore, the proper description of stress-dilatancy with the inclusion of fabric information is a basic requisite for accurately modelling the stress-strain behaviour of sand leading to strain localization, see Wan & Guo (2001a). Stress dilatancy theories based on macroscopic observations can be traced as far back to the early works of Rowe (1962). While the importance of confinement, density and stress path has been clearly demonstrated (
Microscopic study on stress-strain relation of granular materials
Chinese Science Bulletin, 2009
A biaxial shearing test on granular materials is numerically simulated by distinct element method (DEM). The evolution of the microstructures of granular materials during isotropic compression and shearing is investigated, on which a yield function is derived. The new yield function has a similar form as the one used in the modified Cam-clay model and explains the yield characteristics of granular materials under the isotropic compression and shear process through the change of the contact distribution N(θ) defining the contacts at particle contact angle θ.
EFFECT OF PARTICLE SIZE ON THE SHEAR MODULUS OF GRANULAR SOIL
Granular materials such as soil are inherently discrete and their behavior is very complex. Understanding behavior of such materials under cyclic loading is intricate. Traditionally, continuum principles are employed to study the deformation of soil by geotechnical engineers. But, discontinuous nature of soil is required to be considered to understand micro features such as anisotropy, dilatancy, shear localization etc. Also the strength loss when subjected to cyclic loading is affected by particle size, shape and its distribution. In this paper 3D discrete element modeling of cyclic triaxial test was carried out with respect to different particle size distribution and void ratios under drained condition. This study evaluates the dependence of shear modulus on particle distribution.
Deformation Behavior of Sands under Cyclic Loading-A Micro-Structural Approach
1988
16. SUPP'. :MENTARY NOTATION 17. COSATI CODES 1S. SUBJECT TERMS (Continue on reverse if neceusary and identiOy by block number) FIELD GROUP SUB-GROUP .--C ranular Mechanics, Constitutive Law, Packing Structure, / Soil Fabric, Pandom Packings, Soil Moduli, Structural Anisotrop 19. ABST ACT (continue on reverse if necessary and identify by block number)
Stress-stress modelling for heterogeneous granular materials based on micromechanics
1995
The objective of this research is to develop a micromechanics theory for granular material considering the effects of micro-structure. This type of micro-structural based constitutive theory is useful in many fields of studies such as in the mechanics of soil, powder, composite and ceramic. The specific efforts are focused in the following four different areas: (1) descriptions of micro-structure, (2) micro-macro relationship, (3) classes of micromechanics constitutive theory, and (4) contact law of the inter-particle binder. These four areas are the fundamental elements to the construction of a micromechanics theory for granular media. Particular attention will be given to the effect of heterogeneity in micro-structure on the micro-macro mechanical behavior. The nature of this investigation is focused on theoretical development. The developed theory is evaluated by experimental and computer simulation results.
Micro–macro analysis of granular material behavior along proportional strain paths
Continuum Mechanics and Thermodynamics, 2014
When granular materials are subjected to proportional strain loading paths, they manifest a variety of behaviors depending on the initial void ratio of the specimen as well as the imposed dilatancy/contractancy rate. In some cases, the stress components may vanish over the duration of the test, and the specimen may progressively liquefy. To investigate this behavior, the authors have developed a kinematic approach to be deployed in two parts. First, numerical simulations are performed by means of a discrete element method. Secondly, two micromechanical models have corroborated the DEM results. The performance of these models may explain a number of microstructural mechanisms responsible for the macroscopic constitutive behavior.
Development of micromechanical models for granular media
Granular Matter, 2007
Micromechanical analysis has the potential to resolve many of the deficiencies of constitutive equations of granular continua by incorporating information obtained from particle-scale measurements. The outstanding problem in applying micromechanics to granular media is the projection scheme to relate continuum variables to particle-scale variables. Within the confines of a projection scheme that assumes affine motion, contact laws based on binary interactions do not fully capture important instabilities. Specifically, these contact laws do not consider mesoscale mechanics related to particle group behaviour such as force chains commonly seen in granular media. The implications of this are discussed in this paper by comparison of two micromechanical constitutive models to particle data observed in computer simulations using the discrete element method (DEM). The first model, in which relative deformations between isolated particle pairs are projected from continuum strain, fails to deliver the observed behaviour. The second model accounts for the contact mechanics at the mesoscale (i.e. particle group behaviour) and, accordingly, involves a nonaffine projection scheme. In contrast with the first, the second model is shown to display strain softening behaviour related to dilatancy and produce realistic shear bands in finite element simulations of a biaxial test. Importantly, the evolution of microscale variables is correctly replicated. This paper is dedicated to Professor Ching S. Chang on the occasion of his 60th birthday.