On the mechanics of meso-scale structures in two-dimensional granular materials

Zhu, Huaxiang; Veylon, Guillaume; Nicot, François; Darve, Félix

doi:10.1080/19648189.2016.1229229

Cited by 14 publications

(7 citation statements)

References 52 publications

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“…Overcoming the dynamical barriers that separate the metastable regions in the conformational landscape requires an expenditure of energy. In this context, the propensity for BFCs to traverse a dynamical barrier, escaping a metastable region to inhabit another, is entirely consistent with past findings that showed these failure events are accompanied by bursts in kinetic energy, dissipation and mesoscale nonaffine deformation [1,3,4,6,8,12].…”

Section: Resultssupporting

confidence: 88%

Self-organization in the localised failure regime: metastable attractors and their implications on force chain functionality

2017

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In transitive metastable chaotic dynamical systems, there are no invariant neighbourhoods in the phase space. The best that one can do is look for metastable or almost-invariant (AI) regions as a means to decompose the system into its basic self-organising building blocks. Here we study the metastable dynamics of a dense granular material embodying strain localization in 3D from the perspective of its conformational landscape: the state space of all observed conformations as defined by the local topology of individual grains relative to their first ring of contacting neighbors. We determine the metastable AI sets that divide this conformational landscape, such that grain rearrangements from one conformation to another conformation in the same AI set occurs with high probability: by contrast, grain rearrangements involving conformational transitions between AI sets are unlikely. The great majority of conformational transitions are identity transitions: grains rearrange and exchange contacts to preserve those topological properties with the greatest influence on cluster stability, namely, the number of contacts and 3-cycles. Force chains show a clear preference for that AI set with the most number of accessible and highly connected conformations. Here force chains continually explore the conformational landscape, wandering from one rarely inhabited conformation to another. As force chains become overloaded and buckle, the energy released enables member grains to overcome the high dynamical barriers that separate metastable regions and subsequently escape one region to enter another in the conformational landscape. Thus, compared to grains locked in stable force chains, those in buckling force chains, confined to the shear band, show a greater propensity for not only non-identity transitions within each metastable region but also inter-transitions between metastable regions.

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Section: Resultssupporting

confidence: 88%

Self-organization in the localised failure regime: metastable attractors and their implications on force chain functionality

2017

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“…This confining quality is dependent on the properties of force chains surrounding structures and, in particular, on their density, because a higher density provides a better confinement for force chain stability. As a result, the soil density substantially drives the behavior of force chains and the soil fabric by influencing force chain confinement conditions . As dilation develops after the stress peak is reached in the soil, especially within the localized zone, more and more force chains show dysfunction in the principal and neighboring directions based on a lack of reliable supporters.…”

Section: Microscale Propertiesmentioning

confidence: 99%

“…As a result, the soil density substantially drives the behavior of force chains and the soil fabric by influencing force chain confinement conditions. 51,54 As dilation develops after the stress peak is reached in the soil, especially within the localized zone, more and more force chains show dysfunction in the principal and neighboring directions based on a lack of reliable supporters. This rationally results in chronic α-zone extension.…”

Section: Soil Fabricmentioning

confidence: 99%

Observations on fabric evolution to a common micromechanical state at the soil‐structure interface

Zhu

Zhou

Jing

et al. 2019

Num Anal Meth Geomechanics

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Summary The fabric plays an important role in the mechanical behavior of granular material. The aim of this paper is to investigate the evolution of fabric in a soil‐structure interface (SSI) to a large shearing in an effort to clarify whether and how this form of fabric evolution can lead to a common microstructure. Using the discrete element method (DEM), two‐dimensional (2D) numerical interface shear tests were carried out, and certain macromechanical and micromechanical properties were exploited. All samples exhibited prominently localized strain in a zone covering the structure's surface (named the localized zone), and much lower density and higher soil fabric anisotropy levels were found inside this zone than outside it. Disregarding different initial void ratios, a common critical state microstructure was observed in large shear deformations of soil samples, with essentially the same fabric arrangement in terms of contact orientation and internal force transmission. Due to the systematic forming, buckling, and collapsing of force chains, an angular zone (called an α‐zone), in which contact density was sluggish to varying degrees, appeared and extended around the main direction of the distribution of contact orientation inside the localized zone. The gradual deterioration of the force chains' stability, as a result of an increasing void ratio, seemed to drive the α‐zone's extension and lead to the rare variation of microstructures in the critical state.

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“…In the past, various homogenisation methods are developed to derive micro‐macro relationships of granular materials, such as Voigt's hypothesis ( kinematic assumption ), Reuss's hypothesis ( static assumption ) , best‐fit hypothesis , and Piece‐wide fit hypothesis. Some recent works aimed at defining a relevant mesoscale to link continuum‐based mechanics at the macroscopic scale, precisely to circumvent the noncontinuum microscopic characteristics at the contact scale.…”

Section: Introductionmentioning

confidence: 99%

A hybrid calibration approach to Hertz‐type contact parameters for discrete element models

Feng

Zhao

et al. 2020

Num Anal Meth Geomechanics

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This study aims at providing a hybrid calibration framework to estimate Hertztype contact parameters (particle-scale shear modulus and Poisson ratio) for both two-dimensional and three-dimensional discrete element modelling (DEM). On the basis of statistically isotropic granular packings, a set of analytical formulae between macroscopic material parameters (Young modulus and Poisson ratio) and particle-scale Hertz-type contact parameters for granular systems are derived under small-strain isotropic stress conditions. However, the derived analytical solutions are only estimated values for general models.By viewing each DEM modelling as an implicit mathematical function taking the particle-level parameters as independent variables and employing the derived analytical solutions as the initial input parameters, an automatic iterative scheme is proposed to obtain the calibrated parameters with higher accuracies. Considering highly nonlinear features and discontinuities of the macro-micro relationship in Hertz-based discrete element models, the adaptive moment estimation algorithm is adopted in this study because of its capacity of dealing with noise gradients of cost functions. The proposed method is validated with several numerical cases including randomly distributed monodisperse and polydisperse packings. Noticeable improvements in terms of calibration efficiency and accuracy have been made. K E Y W O R D Sadaptive moment estimation, calibration, constitutive law, discrete element method, Hertz-Mindilin contact model, nonlinear elastic model

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On the mechanics of meso-scale structures in two-dimensional granular materials

Cited by 14 publications

References 52 publications

Self-organization in the localised failure regime: metastable attractors and their implications on force chain functionality

Self-organization in the localised failure regime: metastable attractors and their implications on force chain functionality

Observations on fabric evolution to a common micromechanical state at the soil‐structure interface

A hybrid calibration approach to Hertz‐type contact parameters for discrete element models

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