scholarly journals Prediction of Shear Localisation in Granular Materials based on a Critical State Non-coaxial Model

2019 ◽  
Vol 92 ◽  
pp. 16006 ◽  
Author(s):  
Hansini Mallikarachchi ◽  
Kenichi Soga
Keyword(s):  
Granular Materials ◽  
Plane Strain ◽  
Critical State ◽  
Progressive Failure ◽  
Shear Bands ◽  
State Parameter ◽  
Biaxial Compression ◽  
Compression Tests ◽  
Principal Axes ◽  
Shear Localisation

Experimental evidence indicates that the shear localisation acts as a precursor to the failure in biaxial compression tests of granular materials. Once formed they are persistent and lead to progressive failure of most geotechnical structures. It is generally accepted that the primary mode of deformation within these shear bands is simple shear which is accompanied by rotation of principal axes. Hence, the conventional plasticity theories based on the assumption of coaxility is not sufficient to describe the behaviour within those shear bands. This paper highlights the influence of the non-coaxility on the initiation and orientation of shear bands in both drained and undrained sand. The con-coaxial plasticity theory is integrated into a critical state constitutive model enriched with the state parameter concept. The model is capable of taking account of the variation of lode angle under plane strain condition. Numerical plane strain biaxial compression tests are conducted to observe the effect of non-coaxility on shear localisation. Bifurcation criteria based on the acoustic tensor are checked to predict the onset and inclination of the shear band. Predictions from the non-coaxial model are compared with those of coaxial model. The influence of the initial void ratio for the formation of shear bands is explored. Results are compared qualitatively with experimental observations.

scholarly journals A Constitutive Model for Locally Drained Shear Bands in Globally Undrained Dense Sand

2019 ◽  
Vol 92 ◽  
pp. 16005
Author(s):  
Hansini Mallikarachchi ◽  
Kenichi Soga
Keyword(s):  
Shear Band ◽  
Constitutive Model ◽  
Bifurcation Analysis ◽  
Shear Bands ◽  
Constitutive Relationship ◽  
Excess Pore Pressure ◽  
Biaxial Compression ◽  
Compression Tests ◽  
Equilibrium Equations ◽  
Dense Sand

When saturated granular materials which are dilative in nature are subjected to the undrained deformation, their strength increases due to the generation of negative excess pore pressure. This phenomenon is known as dilative hardening and can be witnessed in saturated dense sand or rocks during very fast loading. However, experimental evidence of undrained biaxial compression tests of dense sand shows a limit to this dilative hardening due to the formation of shear bands. There is no consensus in the literature about the mechanism which triggers these shear bands in the dense dilative sand under isochoric constraint. The possible theoretical reasoning is the local drainage inside the specimen under the globally undrained condition, which is challenging to be monitored experimentally. Hence, both incept of localisation and post-bifurcation of the saturated undrained dense sand demand further numerical investigation. Pathological mesh dependency hinders the ability of the finite element method to represent the localisation without advanced regularisation methods. This paper attempt to provide a macroscopic constitutive behaviour of the undrained deformation of the saturated dense sand in the presence of a locally drained shear band. Discontinuation of dilatant hardening due to partial drainage between the shear band and the adjacent material is integrated into the constitutive model without changing governing equilibrium equations. Initially, a classical bifurcation analysis is conducted to detect the inception and inclination of the shear band based on the underlying drained deformation. Then a post-bifurcation analysis is carried out assuming an embedded drained or partially drained shear band at gauss points which satisfy bifurcation criterion. The smeared shear band approach is utilised to homogenise the constitutive relationship. It is observed that the dilatant hardening in the saturated undrained dense sand is reduced considerably due to the formation of shear bands.

Mobilized strength components of Athabasca oil sand in triaxial compression

1999 ◽  
Vol 36 (4) ◽  
pp. 718-735 ◽  
Author(s):  
Ron CK Wong
Keyword(s):  
Critical State ◽  
Triaxial Compression ◽  
Shear Banding ◽  
Shear Bands ◽  
Compression Tests ◽  
Oil Sand ◽  
Shear Dilation ◽  
X Ray Imaging ◽  
Microscopy Techniques ◽  
Triaxial Compression Tests

Dense uncemented Athabasca oil sand specimens exhibit unusually high peak strength, dilation with severe softening, and residual strength in drained triaxial compression tests. Computer tomography scanning, X-ray imaging, and scanning electron microscopy techniques are used to examine the microstructural features of the sheared specimens, such as interlocked structure, shear-banding pattern, and porosity distributions inside and outside shear bands. The characteristics of these microstructural features are used to explain the macrodeformation responses observed in the triaxial compression tests. Mobilization of strength components derived from interlocked structure, dilation, rolling, and critical state are analyzed for pre-peak, post-peak softening, and residual states.Key words: oil sand, interlocked structure, shear dilation, shear band, critical state.

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

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
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.

scholarly journals Soil Particle Movement and Shear Band Development during Plane Strain Compression

2019 ◽  
Vol 92 ◽  
pp. 06006
Author(s):  
Junggeun Hwang ◽  
Hoe I. Ling
Keyword(s):  
Shear Band ◽  
Failure Mechanism ◽  
Plane Strain ◽  
Shear Failure ◽  
Shear Bands ◽  
Vertical Direction ◽  
Plane Strain Compression ◽  
Soil Specimen ◽  
Compression Tests ◽  
Soil Particles

Most geotechnical structures failed by formation and development of shear bands in soils. Thus, shear deformation and shear bands development evaluation are necessary to understand shear failure mechanism. During shearing, deformation behaviour analysis for soil particles within entire soil specimen are evaluated to understand the soil behaviour and shear strength characteristics. In this paper, a series of plane strain compression tests using Nevada sand and Ottawa sand were conducted to identify the shear strain and shear failure mechanism. With the results of plane strain compression tests, image analyses using Particle Image Velocimetry (PIV) were carried out in order to measure the change in position of soil particles and shear bands development. Deformation vectors and contours were constructed to see the entire deformation mechanism in the soil specimen. During shearing, shear band was identified after peak stress and most visually distinctive at residual state. However, shear band started to develop invisibly immediately after starting loading and this invisible development was able to be observed by horizontal and vertical movement analyses of PIV. Soil particles moved actively in horizontal and vertical direction to generate shear band in the beginning of shearing. After development of shear band, soil particles moved along the shear band.

Critical state strength parameters of saturated clays from the modified Cam clay model

1999 ◽  
Vol 36 (5) ◽  
pp. 876-890 ◽  
Author(s):  
Ming-Fang Chang ◽  
Cee Ing Teh ◽  
LaiFa Cao
Keyword(s):  
Plane Strain ◽  
Critical State ◽  
Triaxial Compression ◽  
Compression Tests ◽  
Strength Parameters ◽  
State Strength ◽  
Modified Cam Clay ◽  
Undrained Strength ◽  
Compression Condition ◽  
Cam Clay

The evaluation of critical state strength parameters is important, especially with the introduction of limit state design. The modified Cam clay (MCC) model is often used, but it is suitable mainly for evaluating the critical state strength parameters from triaxial compression tests on isotropically consolidated soils. The initial stress condition of a natural soil is usually anisotropic, and the stress paths imposed by external loading could deviate from that of a simple triaxial compression. The use of MCC in practice deserves careful consideration. This paper describes a proposed extension of the MCC model for the evaluation of critical state strength parameters from undrained triaxial and plane strain tests on anisotropically consolidated clays. Using Lade's failure criterion and the plastic potential of MCC, a generalized yield surface is determined and the relationships between the critical state internal friction angles from various triaxial and plane strain tests are obtained. By relating the isotropic overconsolidation ratio to the conventional overconsolidation ratio (OCR), a procedure is suggested for the prediction of critical state undrained shear strength (su) for clays. The undrained strength normalized by the preconsolidation pressure is not a constant but a function of the angle of internal friction and the OCR. For overconsolidated clay, the predicted undrained strength ratio (su/σVO) for the triaxial compression condition is larger than that for the plane strain compression condition. Comparisons of predicted results with published data indicate that the procedure is applicable to various compression tests on normally and lightly to moderately overconsolidated clays. Key words: stress anisotropy, clay, constitutive model, critical state, laboratory test, shear strength parameters.

Modeling Fracturing in Rock Using a Modified Discrete Element Method with Plasticity

2010 ◽  
Vol 452-453 ◽  
pp. 861-864 ◽  
Author(s):  
Haitham Alassi ◽  
Rune Holt
Keyword(s):  
Shear Bands ◽  
Discrete Element ◽  
Initial Crack ◽  
Reservoir Rock ◽  
Biaxial Compression ◽  
Compression Tests ◽  
Direct Tension ◽  
Direct Tension Test ◽  
New Development ◽  
Element Approach

In this contribution we present more developments in the modified discrete element approach (MDEM) which was proposed to model fractures propagation in reservoir rock during production and fluid injection. The new development in this paper includes adding plasticity which allows the material to go into plastic deformation before initiating fractures. Several numerical tests are performed which mimic the real lab tests usually perform on rock samples, this includes direct tension test with initial crack to model crack propagation, and several biaxial compression tests to model the development of shear bands.

Progressive failure mechanism in granular materials subjected to an alternant active and passive trapdoor

2021 ◽  
Vol 28 ◽  
pp. 100529
Author(s):  
Yu Zhao ◽  
Quanmei Gong ◽  
Yaojie Wu ◽  
Zhiyao Tian ◽  
Shunhua Zhou ◽  
...  
Keyword(s):  
Granular Materials ◽  
Failure Mechanism ◽  
Progressive Failure

Characteristics of the Deformed and Recrystallised Grains Obtained after Hot Plane Strain Compression of a Model Fe-30wt%Ni Alloy

2004 ◽  
Vol 467-470 ◽  
pp. 21-26 ◽  
Author(s):  
F. Bai ◽  
P. Cizek ◽  
Eric J. Palmiere ◽  
Mark W. Rainforth
Keyword(s):  
Plane Strain ◽  
Crystallographic Texture ◽  
Hot Deformation ◽  
Electron Backscatter Diffraction ◽  
Orientation Dependence ◽  
Plane Strain Compression ◽  
Formation Mechanisms ◽  
Subgrain Structure ◽  
Compression Tests ◽  
Texture Characteristics

The development of physically-based models of microstructural evolution during hot deformation of metallic materials requires knowledge of the grain/subgrain structure and crystallographic texture characteristics over a range of processing conditions. A Fe-30wt%Ni based alloy, retaining a stable austenitic structure at room temperature, was used for modelling the development of austenite microstructure during hot deformation of conventional carbon-manganese steels. A series of plane strain compression tests was carried out at a temperature of 950 °C and strain rates of 10 s-1 and 0.1 s-1 to several strain levels. Evolution of the grain/subgrain structure and crystallographic texture was characterised in detail using quantitative light microscopy and highresolution electron backscatter diffraction. Crystallographic texture characteristics were determined separately for the observed deformed and recrystallised grains. The subgrain geometry and dimensions together with the misorientation vectors across sub-boundaries were quantified in detail across large sample areas and the orientation dependence of these characteristics was determined. Formation mechanisms of the recrystallised grains were established in relation to the deformation microstructure.

Sign in / Sign up

Export Citation Format

Share Document