An efficient flexible membrane boundary condition for DEM simulation of axisymmetric element tests

Khoubani, Ali; Evans, T. Matthew

doi:10.1002/nag.2762

Cited by 27 publications

(9 citation statements)

References 48 publications

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“…However, it is still observed that models with a rigid wall boundary slightly underestimate the deviator stress in the post-elastic zone compared to the simulations with a flexible membrane boundary. Similar conclusions are obtained in [10,[18][19]. The mechanism responsible for this difference is that the end restraint in our models with the flexible boundary acts as an additional confinement at the ends of the specimen, preventing the soil from moving outwards freely.…”

Section: Stress-strain Relationsupporting

confidence: 81%

“…The method was initially reported by Zhao and Evans [9,11], and later Ergenzinger et al [8] reported a similar simulation method. Khoubani and Evans [10] improved the deformable ability of stacked-wall boundary further. This method is conceptually simple and easy to be implemented.…”

Section: Stacked Wallsmentioning

confidence: 99%

“…To accurately apply the hydrostatic confining stress but at the same time to allow free deformation of the membrane boundary are two main difficulties imposed to the DEM modelling of triaxial tests with latex/rubber membranes. Existing DEM models 5 that consider flexible membrane can be classified into four categories: stacked walls method [8][9][10][11], periodic boundary [12], equivalent force algorithms [7,[13][14][15], and particle membrane method [5,[16][17][18][19][20].…”

Section: Overview Of Flexible Membrane Simulationmentioning

confidence: 99%

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Discrete element modelling of flexible membrane boundaries for triaxial tests

Feng

Wang

et al. 2019

Computers and Geotechnics

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The discrete element modelling (DEM) of triaxial tests plays a critical role in 2 unveiling fundamental properties of particulate materials, but the numerical 3 implementation of a flexible membrane boundary for the testing still imposes 4 problems. In this study, a robust algorithm was proposed to reproduce a flexible 5 membrane boundary in triaxial testing. The equivalence of strain energy enables the 6 particle-scale parameters representing the flexible membrane to be directly 7 determined from the real geometric and material parameters of the membrane. Then 8 the proposed flexible membrane boundary was implemented in the context of discrete 9 element simulation of triaxial testing and was validated with laboratory experiments. 10 Furthermore, comparisons of triaxial tests with flexible and rigid boundaries were 11 performed from macro-scale to meso-scale. The results show that the boundary 12 condition has limited influences on the stress-strain behaviour but a relatively large 13 impact on the volumetric change, the failure mode, the distribution of contact forces, 14 and the fabric evolution of particles in the specimen during triaxial testing. 15

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Section: Stress-strain Relationsupporting

confidence: 81%

Section: Stacked Wallsmentioning

confidence: 99%

Section: Overview Of Flexible Membrane Simulationmentioning

confidence: 99%

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Discrete element modelling of flexible membrane boundaries for triaxial tests

Feng

Wang

et al. 2019

Computers and Geotechnics

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“…Because the sample in the triaxial test received less confinement from the lateral direction, T1 had a much lower peak stress and gentler stress softening than P1 and did not appear in the shear zone to as concentrated a degree as the latter. Khoubani and Evans performed the DEM conventional triaxial test with the cylinder flexible boundary modelled by many force‐controlled planar walls. They produced the similar shape of stress and volumetric curves to those shown in Figure for both presented dense and loose samples.…”

Section: Macro‐ and Micro‐mechanical Responsesmentioning

confidence: 99%

“…Building the membrane by bonding particles, although a widely adopted technique, causes the following problems: (1) the modelling complexity involved in shaping the membrane by particles; (2) difficulties in applying normal stress to the membrane particles according to the surface geometry; (3) an associated but unnatural friction between the membrane and soil caused by the surface asperity of the particulate membrane; and (4) an unknown relationship between the bonding parameters among membrane particles (ie, normal and shear stiffness) and the elastic parameters of the membrane (Young's modulus E and Poisson ratio v ). Alternatively, some researchers have constructed the membrane using many tiny pieces of rigid wall, served by constantly applied normal stress, to implement the hydrostatic confinement . When the membrane is separated into detached pieces of walls, this method lacks interaction and compatibility between neighbouring membrane elements, meaning that it is unable to accurately reproduce the behaviour of the membrane as an integrated entity.…”

Section: Introductionmentioning

confidence: 99%

A novel coupled FDM‐DEM modelling method for flexible membrane boundary in laboratory tests

Zhu

Yin

Zhang

2019

Num Anal Meth Geomechanics

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Difficulties are involved in discrete element method (DEM) modelling of the flexible boundary, that is, the membranes covering the soil sample, which can be commonly found in contemporary laboratory soil tests. In this paper, a novel method is proposed wherein the finite difference method (FDM) and DEM are coupled to simulate the rubber membrane and soil body, respectively. Numerical plane strain and triaxial tests, served by the flexible membrane, are implemented and analysed later. The effect of the membrane modulus on the measurement accuracy is considered, with analytical formulae derived to judge the significance of this effect. Based on an analysis of stress-strain responses and the grain rotation field, the mechanical performances produced by the flexible and rigid lateral boundaries are compared for the plane strain test. The results show that (1) the effect of the membrane on the test result becomes more significant at larger strain level because the membrane applies additional lateral confining pressure to the soil body; (2) the tested models reproduce typical stress and volumetric paths for specimens with shear bands; (3) for the plane strain test, the rigid lateral boundary derives a much higher peak strength and larger bulk dilatation, but a similar residual strength, compared with the flexible boundary. The latter produces a more uniform (or 'diffuse') rotation field and more mobilised local kinematics than does the former. All simulations show that the proposed FDM-DEM coupling method is able to simulate laboratory tests with a flexible boundary membrane. K E Y W O R D Sdiscrete element method, finite difference method, flexible boundary, plane strain test, shear band, triaxial test

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Effect of flexible membrane in triaxial test on the mechanical behaviour of rockfill material using Discrete Element Method

Asadi,

Disfani,

Ghahreman-Nejad

et al. 2024

Granular Matter

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The investigation of rockfill materials poses challenges due to their large particle size, associated high cost, and long laboratory testing duration. As a result, empirical correlations based on historical experimental studies are commonly used to design and analyse rockfill structures. However, the extensive use of rockfill in a wide range of applications and limited understanding of its mechanical behaviour emphasize the need for further research. These make it necessary to develop a robust technique capable of capturing key parameters such as particle shape and breakage, allowing for the simulation and study of large-scale assemblies with realistic boundary conditions. Given that the behaviour of rockfill is highly scale-dependent, primarily due to particle breakage, the simplified laboratory tests on the scaled-down assemblies can be misleading. Particle breakage is a fundamental phenomenon in the mechanical behaviour of rockfill and significantly affects shear strength, deformability, and porosity under different stress levels. The particle breakage is influenced by factors such as the rockfill’s maximum particle size, mineralogy, particle shape, gradation, and confining stresses. This study adopts a computationally efficient breakage method called the Modified Particle Replacement Method (MPRM) based on the Discrete Element Method. A Tile-Based Flexible Membrane (TBFM) for triaxial test modelling has been developed by employing segmental rectangular walls to create a deformable membrane. The effects of critical parameters, including particle shape, confining stress, membrane resolution, degree of flexibility, and the characteristic strength of the particles, are examined. The findings of the combined MPRM-TBFM approach demonstrate the significant influence of membrane flexibility on volumetric-related behaviour. Graphical Abstract

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An efficient flexible membrane boundary condition for DEM simulation of axisymmetric element tests

Cited by 27 publications

References 48 publications

Discrete element modelling of flexible membrane boundaries for triaxial tests

Discrete element modelling of flexible membrane boundaries for triaxial tests

A novel coupled FDM‐DEM modelling method for flexible membrane boundary in laboratory tests

Effect of flexible membrane in triaxial test on the mechanical behaviour of rockfill material using Discrete Element Method

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