Effect of Grain Orientation Distribution on Anisotropy of Idealized Granular Materials

Abstract. The regular grain orientation of granular materials is a common phenomenon in nature. Based on the research of grain shape effect on mechanical property of granular materials, two kinds of idealized shape grain (kind of long rod and square) assemblies with different grain orientation were studied by simulated biaxial compression test using Discrete Element Method. The significant orientation which can be computed as the mean value of all grain orientation is introduced to represent the orientation regularity of granular materials. In order to study the anisotropy, the mobilized friction angle and volumetric strain of assemblies with different significant orientation were obtained under both vertical and horizontal loading. The results show that the regular orientation of grains influences the movement such as motion and rotation obviously; with the increasing of significant orientation, peak mobilized friction angle of long rod grain assembly gradually increases under horizontal loading, and decreasing under vertical loading.

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DEM Simulation of Biaxial Compression Experiments of Inherently Anisotropic Granular Materials and the Boundary Effects

Journal of Applied Mathematics ◽

10.1155/2013/394372 ◽

2013 ◽

Vol 2013 ◽

pp. 1-13 ◽

Cited By ~ 2

Author(s):

Zhao-Xia Tong ◽

Lian-Wei Zhang ◽

Min Zhou

Keyword(s):

Boundary Conditions ◽

Granular Materials ◽

Friction Angle ◽

Boundary Effects ◽

Biaxial Compression ◽

Deformation Pattern ◽

Compression Tests ◽

Stress Strain ◽

Particle Assembly ◽

Strain Relationship

The reliability of discrete element method (DEM) numerical simulations is significantly dependent on the particle-scale parameters and boundary conditions. To verify the DEM models, two series of biaxial compression tests on ellipse-shaped steel rods are used. The comparisons on the stress-strain relationship, strength, and deformation pattern of experiments and simulations indicate that the DEM models are able to capture the key macro- and micromechanical behavior of inherently anisotropic granular materials with high fidelity. By using the validated DEM models, the boundary effects on the macrodeformation, strain localization, and nonuniformity of stress distribution inside the specimens are investigated using two rigid boundaries and one flexible boundary. The results demonstrate that the boundary condition plays a significant role on the stress-strain relationship and strength of granular materials with inherent fabric anisotropy if the stresses are calculated by the force applied on the wall. However, the responses of the particle assembly measured inside the specimens are almost the same with little influence from the boundary conditions. The peak friction angle obtained from the compression tests with flexible boundary represents the real friction angle of particle assembly. Due to the weak lateral constraints, the degree of stress nonuniformity under flexible boundary is higher than that under rigid boundary.

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Assessment of the range of variation of Nγ from 60 estimation methods for footings on sand

Canadian Geotechnical Journal ◽

10.1139/cgj-2012-0426 ◽

2013 ◽

Vol 50 (7) ◽

pp. 793-800 ◽

Cited By ~ 12

Author(s):

Edgar Giovanny Diaz-Segura

Keyword(s):

Friction Angle ◽

Standard Penetration Test ◽

Estimation Methods ◽

Penetration Test ◽

In Situ Tests ◽

Vertical Loading ◽

Simplified Method ◽

Bearing Capacity Factor ◽

Range Of Variation

The range of variation of the bearing capacity factor, Nγ, was assessed using 60 estimation methods for rough footings on sand subjected to static vertical loading. The influence on the Nγ values of the use of correlations for the estimation of the friction angle, [Formula: see text], derived from in situ tests was also assessed. The analysis shows a marked dependency on the methods used to determine Nγ, showing differences for the same [Formula: see text] values of up to 267% between estimated values. Uncertainty in the estimation of [Formula: see text], due to the use of correlations with in situ tests, leads to a range of variation for Nγ higher than that seen using the 60 estimation methods. Finally, given the regular use of the in situ standard penetration test (SPT) on sands, and based on a series of analyses using finite elements, a simplified method in terms of the SPT N-values is proposed for estimation of Nγ in footings on sands.

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Micro-Deformation Mechanism of Granular Materials under Different Boundary Conditions Based on DEM Simulation

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.170-173.3361 ◽

2012 ◽

Vol 170-173 ◽

pp. 3361-3366

Author(s):

Zhao Xia Tong ◽

Min Zhou ◽

Yang Ping Yao

Keyword(s):

Boundary Condition ◽

Granular Materials ◽

Biaxial Compression ◽

Special Focus ◽

Particle Rotation ◽

Axis Orientation ◽

Dem Simulation ◽

Steel Bars ◽

Strain Relationship ◽

Micro Deformation

Series of biaxial compression simulations are carried out to investigate the effects of boundary condition on the deformation of granular materials by using DEM. The parameters used in DEM are validated by the biaxial compression experiments on elliptical steel bars. The effects of boundary condition on the stress-strain relationship are analyzed. And special focus are put in the analysis of particle displacement, particle rotation, void distribution, particle long axis orientation and contact force with the development of deformation.

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The critical state friction angle of granular materials: does it depend on grading?

Acta Geotechnica ◽

10.1007/s11440-017-0581-x ◽

2017 ◽

Vol 13 (3) ◽

pp. 535-547 ◽

Cited By ~ 17

Author(s):

J. Yang ◽

X. D. Luo

Keyword(s):

Granular Materials ◽

Critical State ◽

Friction Angle

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EVOLUTION OF THE CARBON NANOTUBE BUNDLE STRUCTURE UNDER BIAXIAL AND SHEAR STRAINS

Facta Universitatis Series Mechanical Engineering ◽

10.22190/fume201005043r ◽

2020 ◽

pp. 525

Author(s):

Leysan Kh. Rysaeva ◽

Dmitry V. Bachurin ◽

Ramil T. Murzaev ◽

Dina U. Abdullina ◽

Elena A. Korznikova ◽

...

Keyword(s):

Carbon Nanotube ◽

Shear Strain ◽

Cross Sections ◽

Degrees Of Freedom ◽

Shear Bands ◽

Volumetric Strain ◽

Structural Evolution ◽

Biaxial Compression ◽

Chain Model ◽

Nanotube Bundle

Close packed carbon nanotube bundles are materials with highly deformable elements, for which unusual deformation mechanisms are expected. Structural evolution of the zigzag carbon nanotube bundle subjected to biaxial lateral compression with the subsequent shear straining is studied under plane strain conditions using the chain model with a reduced number of degrees of freedom. Biaxial compression results in bending of carbon nanotubes walls and formation of the characteristic pattern, when nanotube cross-sections are inclined in the opposite directions alternatively in the parallel close-packed rows. Subsequent shearing up to a certain shear strain leads to an appearance of shear bands and vortex-like displacements. Stress components and potential energy as the functions of shear strain for different values of the biaxial volumetric strain are analyzed in detail. A new mechanism of carbon nanotube bundle shear deformation through cooperative, vortex-like displacements of nanotube cross sections is reported.

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