The combined scaled boundary finite-discrete element method : Grain breakage modelling in cohesion-less granular media
- Authors: Luo, Tao , Ooi, Ean Tat , Chan, Andrew , Fu, Shaojun
- Date: 2017
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 88, no. (2017), p. 199-221
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- Description: A computational technique combining the scaled boundary finite element method (SBFEM) and the discrete element method (DEM) is developed. Both methodologies work in tandem to model two mechanisms i.e. grain-to-grain interaction via DEM; and breakage of individual grains via SBFEM. Both play important roles in characterising the response of granular soils. The combination of the two methods results in some advantages in computational flexibility and implementation in modelling grain breakage in granular materials. Parametric studies demonstrate the method's ability to reproduce stress-strain curves in bi-axial tests of granular rock-fills; and qualitatively predicts characteristics of grain breakage observed in laboratory tests. © 2017 Elsevier Ltd
A quadtree-polygon-based scaled boundary finite element method for crack propagation modeling in functionally graded materials
- Authors: Chen, Xiaojun , Luo, Tao , Ooi, Ean Tat , Ooi, Ean Hin , Song, Chongmin
- Date: 2018
- Type: Text , Journal article
- Relation: Theoretical and Applied Fracture Mechanics Vol. 94, no. (2018), p. 120-133
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- Description: This paper presents a method to improve the computational efficiency of the scaled boundary finite element formulation for functionally graded materials. Both isotropic and orthotropic functionally graded materials are considered. This is achieved using a combination of quadtree and polygon meshes. This hybrid meshing approach is particularly suitable to be used with the SBFEM for functionally graded materials because of the significant amount of calculations required to compute the stiffness matrices of the polygons/cells in the mesh. When a quadtree structure is adopted, most of the variables required for the numerical simulation can be pre-computed and stored in the memory, retrieved and scaled as required during the computations, leading to an efficient method for crack propagation modeling. The scaled boundary finite element formulation enables accurate computation of the stress intensity factors directly from the stress solutions without any special post-processing techniques or local mesh refinement in the vicinity of the crack tip. Numerical benchmarks demonstrate the efficiency of the proposed method as opposed to using a purely polygon-mesh based approach. © 2018 Elsevier Ltd
A 2-D polygon discrete element method and program for simulating rockfill materials
- Authors: Luo, Tao , Ooi, Ean Tat , Chan, Andrew , Fu, Shaojun
- Date: 2017
- Type: Text , Journal article
- Relation: Yantu Lixue/Rock and Soil Mechanics Vol. 38, no. 3 (2017), p. 883-892
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- Description: Every single particle is simulated by a polygon discrete element to capture the realistic shape of rockfill materials. A polygon discrete element method (PDEM) is developed by adopting a simple contact detection program and a polygon/polygon contact model. A linear program is adopted to detect the contact details between polygons. Then the normal contact force is calculated by a potential energy based polygon/polygon normal contact model, and a polygon discrete element calculation method is formed. Based on this method, a program called PDEM is developed to study the interaction between particles and both the translational and rotational motion of every particle from the microscopic view. The effect of micro-properties (e.g. particle shape, size, material properties et al.) on the macro-strength and deformation is enabled. A two-dimensional model test of a coarse aggregate was carried out by PDEM program. The stress and deformation laws consistent with the lab experiment were obtained, and the method and procedure were used to study the effectiveness of the rockfill. © 2017, Science Press. All right reserved.
A combined DEM-SBFEM for modelling particle breakage of rock-fill materials
- Authors: Luo, Tao , Ooi, Ean Tat , Chan, Andrew , Fu, Shaojun
- Date: 2017
- Type: Journal article
- Relation: Yantu Lixue/Rock and Soil Mechanics Vol. 38, no. 5 (2017), p. 1463-1471
- Full Text: false
- Reviewed:
- Description: Both experimental and numerical results demonstrate that particle breakage has significant influence on the macro mechanical response of granular soils. In this study, a novel computational method was proposed to simulate particle breakage phenomenon in granular soils. The proposed method based on the discrete element method (DEM) and the scaled boundary finite element method (SBFEM) has advantages of each method. Individual grains of soil are modelled by a single star-convex polygon with an arbitrary number of sides. The DEM is used to determine the motion of particles and the interaction among particles, whereas the SBFEM is applied to obtain stress states of grains at the end of each time step. Since the SBFEM flexibly describes the morphology of each grain with a single polygon consisting of an arbitrary number of sides, it greatly reduces the necessary computational resources for stress analysis. When the stress state has been confirmed, Hoek-Brown criterion is chosen to determine the 'plastic points' within each particle. Once the ratio of 'plastic points' reaches a predefined threshold, the particle breakage is triggered. As a straight breakage line is assumed for simplification, the particle is split into two when breakage occurs. The newly generated polygons are directly modelled by the DEM and SBFEM without any change of the formulation, and thus this method does not need to predefine sub-particles and re-meshing elements. At last, the feasibility of the newly developed method is verified by a biaxial benchmark test. © 2017, Science Press. All right reserved.