•A detailed FDEM numerical method to simulate mechanical and fracturing responses of heterogeneous geomaterials with irregular inclusions is systematically developed.•A computational geometry method ...named CWSVM is proposed to control mesh quantity and quality.•A signed-distance-field-based discrete element method (SDF-DEM) is employed to approach the natural allocation and orientation of inclusions.•A combined constitutive model is proposed to consider the shearing hardening behaviour for the cohesive elements.•Effects of the interface strength on the mechanical and fracturing behaviours of inclusion-containing geomaterials are extensively discussed.
In this paper, a detailed FDEM approach to simulate the mechanical and fracturing responses of heterogeneous geomaterials with irregular inclusions is systematically developed. The inclusion surface morphology is first obtained through 3D scanning techniques. A computational geometry method, the curvature-weighted sphere Voronoi method (CWSVM), is adopted to control the mesh quantity and quality and ensure the efficiency and accuracy of the FDEM numerical model. A signed-distance-field-based discrete element method (SDF-DEM) is employed to approximate the natural distribution and orientation of inclusions. Heterogeneous geomaterials with large inclusion contents (such as 60% and 70%) are generated effectively and efficiently through this approach. Next, to model the fracturing process, a finite discrete element method (FDEM) model is developed by integrating cohesive elements into the mesh in a fast and efficient manner. In addition, a combined constitutive model is proposed to consider the shear-hardening behaviour of the cohesive elements. The proposed numerical approach is verified through comparison with experimental results, including the shape of inclusions and mechanical responses of geomaterials. The results demonstrate that both satisfactory precision and low calculation costs can be achieved using the proposed algorithm. The consequent simulation performance is verified through comparisons of observations and numerical results with experimental results for failure patterns and mechanical behaviours. In addition, the effects of the strength of the interfaces between the inclusions and matrix on the mechanical and fracturing characteristics of inclusion-containing geomaterials are analysed quantitatively. The mechanical strength decreases rather than increases with increasing content of inclusions when the interface strength is less than the matrix strength.
•CFD-DEM formulation, including heat and mass transfer and long-range forces is described.•Implementation of CFD-DEM in simulation of different processes is discussed.•Different applications, ...including drying, coating, mixing combustion, gasification and etc. are discussed.
With increasing the computational resources, the number of publications about coupled computational fluid dynamics – discrete element method is in the rise in the recent years. This technique is very useful, especially in simulation of fluid-solid flows in process engineering. This paper provides an introduction to CFD-DEM modeling in process engineering systems, including heat and mass transfer and long range forces, and reviews the major researches in simulation of two-phase processes such as drying, coating, granulation, crystallization, chemical reactions (including combustion, gasification and pyrolysis) and mixing. Details of implementing unresolved CFD-DEM in these applications are explained in details and major assumptions and findings are discussed.
•A modelling framework for multi-track, multi-layer and multi-material SLM.•Simulation of multi-material powder deposition in various patterns.•Effect of process parameters on balling effect, keyhole ...and lack of fusion.•Molten pool evolution of multi-material SLM on the same and across different layers.•Modelling of phase migration at the interface between two different materials.
Selective laser melting (SLM) is a promising powder-based additive manufacturing technology due to its capability to fabricate metallic components with complex geometries. While most previous investigations focus on printing with a single material, recent industry-orientated studies indicate the need for multi-material SLM in several high-value manufacturing sectors including medical devices, aerospace and automotive industries. However, understanding the underlying physics in multi-material SLM remains challenging due to the difficulties of experimental observation. In this paper, an integrated modelling framework for multi-track, multi-layer and multi-material SLM is developed to advance the in-depth understanding of this process. The main novelty is in modelling the molten pool evolvement and track morphology of multiple materials deposited on the same and across different layers. Discrete element method (DEM) is employed to reproduce the powder deposition process of multiple materials in different deposition patterns, with particle size distribution imported from a particle size analyser. Various phenomena including balling effect, keyhole depression, and lack of fusion between layers are investigated with different laser energy inputs. As a result of the different thermal properties, several process parameters including energy density and hatch spacing are optimised for different powder materials to obtain a continuous track profile and improved scanning efficiency. The interface between two layers of different materials is visualised by simulation; it was found that the phase migration at the interface is related to the convection flow inside the molten pool, which contributes to the mixing of the two materials and elemental diffusion. This study significantly contributes to the challenging area of multi-material additive manufacturing by providing a greater in-depth understanding of the SLM process from multi-material powder deposition to laser interaction with powders across multiple scanning tracks and different building layers than can be achieved by experimentation alone.
Summary
The combined finite‐discrete element method (FDEM) was originally developed for fracture and fragmentation of brittle materials, more specifically for cementitious and rock‐like materials. In ...this work, a combination of a discrete crack and plastic deformation has been combined and applied to FDEM simulation of fracture. The deformation is described using a FDEM‐specific mechanistic approach with plastic deformation being formulated in material embedded coordinate systems leading to multiplicative decomposition and plastic flow, that is, resolved in stretch space; this is combined with the FDEM fracture and fragmentation criteria. The result and main novelty of the present work is a robust framework for simulation of large strain solid deformation combined with a multiplicative decomposition‐based model that simultaneously involves elasticity, plasticity, and fracture.
The goal of this review paper is to provide a summary of selected discrete element and hybrid finitediscrete element modeling techniques that have emerged in the field of rock mechanics as simulation ...tools for fracturing processes in rocks and rock masses. The fundamental principles of each computer code are illustrated with particular emphasis on the approach specifically adopted to simulate fracture nucleation and propagation and to account for the presence of rock mass discontinuities. This description is accompanied by a brief review of application studies focusing on laboratory-scale models of rock failure processes and on the simulation of damage development around underground excavations.
Based on a combined finite-discrete element method (FDEM), this study builds a coupled thermo-mechanical model (termed FDEM-TM) to simulate thermal cracking of rock. The coupled thermo-mechanical ...model consists of two major parts. In the first part the temperature distribution of the system is analyzed based on the heat conduction equation. In the second part the thermal stress caused by temperature change is added to perform mechanical fracture calculation. Based on these two parts, we can model rock fracture driven by thermo-mechanical coupling. Three examples with analytic solutions are used to verify the correctness of the model in dealing with the problems of steady-state heat conduction, unsteady-state conduction, and thermal-mechanic coupling, respectively. In addition, an example of thermal cracking is also given and compared with the experimental results. The simulation results are in excellent agreement with the analytical solutions or experimental results, verifying the correctness of the coupled thermo-mechanical model to simulate thermal cracking. The proposed method provides a new tool for thermal-mechanical coupling problems in geothermal exploitation.
•An FDEM-based model, FDEM-TM, is proposed for simulating thermal cracking of rock.•FDEM-TM is able to describe thermal-mechanic behaviors in rock.•The proposed method provides a new way for thermal-mechanical coupling problems in geothermal exploitation.
AbstractAggregate occupies at least three-quarters of the volume of asphalt mixture and can significantly affect the performance of pavement. The geometrical morphology influences the slippage and ...interlock among aggregates for resisting and distributing applied loads. In recent years, the discrete-element method (DEM) has been employed for simulation of asphalt mixture structure. This paper introduces an approach for simulation of aggregate and asphalt mixtures using parameterized shape and size gradation. Both the plane geometry factor (PGF) and the section aspect ratio (SAR) were employed to describe the three-dimensional (3D) geometric characteristics of aggregates. A numerical technique of aggregate models was implemented with probabilistic parameters depending on statistical results of PGFs and SARs. The 3D numerical model of asphalt mixtures was assembled with three different components, and was validated by uniaxial compression tests via comparison with the laboratory result. It was found that the PGF and SAR are appropriate to describe the three-dimensional features of aggregate shapes, because a simplified space object can be described by a two-dimensional (2D) graphical projection and a vector scalar corresponding to the space vector. Probability distribution curves of PGFs and SARs between coarse aggregates were in concordance with the Gauss-type function, because their correlation coefficients were all greater than 95%. It was verified that the developed clumping algorithm of aggregates was reasonable in terms of the shape and size gradation. Based on the parallel-bond model and Burger’s model, the results of virtual tests were in good agreement with those of laboratory uniaxial tests. The angularity (PGF) of aggregates has a beneficial effect on the strength and stability of asphalt mixtures, whereas the flat-elongated feature (SAR) has a negative effect on the strength and stability of asphalt mixtures.
•Experimental and numerical study of size effect on concrete in splitting tensile test.•The post-peak behavior of all tested specimens including catastrophic behavior (snap-back).•Cracked specimens ...scanned with micro-CT to study fracture process.•DEM model based on microCT scans with realistic meso-structure.•DEM results captured size/effect on strength and post-peak behavior including snap-back.
The paper describes an experimental and numerical study of size effect on concrete cylindrical specimens in splitting tensile test. Own experimental campaign was performed on specimens with 5 various diameters from D = 74, 105, 150, 192 and 250 mm with hardboard loading strips (distributed load according to standard methods) scaled proportionally to the specimen diameter. The crack opening-control system was applied to obtain the post-peak behaviour of all tested specimens including catastrophic behaviour (snap-back). The tested specimens at a certain point were unloaded and scanned with novel high-resolution micro tomography to analyse the macro cracks and phenomena like aggregate breakage, crack branching etc. at the aggregate level. Based on realistic mesostructure the discrete element method (DEM) 2D model of 3 specimens with diameters of D = 74, 150 and 250 mm were constructed and tested. The fracture was analysed at macro and micro-level in DEM and directly compared with microCT scans. DEM simulations revealed additional information related to the loss of material strength and ductility with increasing specimen size (size effect). The simulation and experimental results were in good agreement.
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