Papers by Keyword: Discrete Element Method (DEM)

Abstract: Selective Laser Sintering (SLS) has recently become one of the fastest growing additive manufacturing processes due to its capability of fabricating metal parts with high dimensional accuracy and surface quality. Physical modeling of this process plays an important role in properly controlling the process parameters of the process. In this paper, we present a 3 dimensional, adaptive discrete element method for simulation of the SLS process on personal computers. The presented method models the laser-powder interaction at particle level, achieving high simulation accuracy while adaptively increasing the discrete element size as local temperatures drop inside the powder bed for improved efficiency. Numerical shape functions are developed for calculating individual particle temperatures at any point during the simulation. Results show that this physical model improves the runtime significantly in virtual simulation of SLS process without loss of simulation accuracy.

Abstract: Pure molybdenum powder material was processed by equal channel angular pressing (ECAP) with different numbers of passes at the temperature of 400 °C and then Vickers microhardness measurements and scanning electron microscopy (SEM) analysis were conducted. The samples were further characterized with electron back scatter diffraction (EBSD) to examine the grain size. These experimental results exhibit that the powder material is well consolidated and the grains are refined by 2 passes of ECAP processing. In addition, discrete element method (DEM) was used to investigate the deformation behaviour of particles as well as the pores between the particles. The deformation of particles, the distribution of residual porosity and the variation of coordination number in pure molybdenum powder material sample during ECAP were obtained in microscopic scale and all the simulation results are well in line with the microstructure evolution.

Abstract: This study presents the numerical simulation of a true triaxial test by means of the discrete element method (DEM). Experimental results performed on Toyoura sand are employed as reference and the calibration methodology is explained. Physical aspects of the real soil, such as the grain size distribution and the relative density, are considered during the generation of the virtual sample. It is shown that the main aspects of the macro-mechanical behaviour of granular soils during compression loading can be fairly represented by the idealised simulations with particles.

Abstract: A generalised approach for the modelling of arbitrary shaped deformable structures in the framework of the discrete element method is presented. Minkowski sums of polytopes and spheres are used to describe the geometry of rounded cylinders and particle facets. In the current formulation, these new elements can be deformable. Their deformation is defined by the set of positions and orientations of their nodes. The elements can be connected to form arbitrary structures, such as grids and membranes. The constitutive behaviour of such connections is defined via an elastic perfectly plastic beam model. Contacts between other not connected structures or particles are detected based on three simple primitives: spheres, cylinders and thick rounded facets. The introduction of a virtual sphere at the contact point not only allows for straightforward contact handling but as well for the use of standard contact models based on sphere–sphere interactions. Hence, there is no need for developing new contact models. The approach is implemented into the open-source framework YADE. The capability of the newly developed approach for the modelling of soil–inclusion problems is presented.

Abstract: The red blood cell (RBC) membrane consists of a lipid bilayer and spectrin-based cytoskeleton, which enclose haemoglobin-rich fluid. Numerical models of RBCs typically integrate the two membrane components into a single layer, preventing investigation of bilayer-cytoskeleton interaction. To address this constraint, a new RBC model which considers the bilayer and cytoskeleton separately is developed using the discrete element method (DEM). This is completed in 2D as a proof-of-concept, with an extension to 3D planned in the future. Resting RBC morphology predicted by the two-layer model is compared to an equivalent and well-established composite (one-layer) model with excellent agreement for critical cell dimensions. A parametric study is performed where area reduction ratio and spring constants are varied. It is found that predicted resting geometry is relatively insensitive to changes in spring stiffness, but a shape variation is observed for reduction ratio changes as expected.

Abstract: In hot rolling, the thermal cyclic of work rolls causes a superficial oxide scale, which plays an important role on the contact friction and wear. The asperities of oxidised strip surface and wear debris slide over the High Speed Steel (HSS) work roll surface which comprises of hard carbides within an iron matrix under high pressure and velocity. Abrasive wear occurs and the particles will be removed from HSS surface. The current study introduces the Discrete Element Method (DEM) to investigate this abrasive wear phenomenon. The model successfully provides a physically based abrasive roll wear predication of HSS work roll with the consideration of carbides and oxide layers. It has been found that the carbide shape in the HSS roll affects the wear significantly, which has not been reported by previous numerical simulations and is the main focus of this research.

Abstract: Laminated glass is widely used to enhance structural functions. The impact fracture behavior of laminated glass is more complicated than that of single glass, because of the combined influences of the large deformation and delamination strengths. In this study, the impact fracture behavior of a laminated glass plate intended for the outside surface of a modern building has been studied by numerical simulations and experiments. This fracture simulation was calculated using a Discrete Element Method (DEM) based on non-continuum mechanics. The laminated glass structures have been optimized for attaining maximum durability against impact fracture based on the response surface method. In the optimum problem, the tensile strength of the interlayer and the adhesive strength between two pieces of glass and the interlayer are taken as the design variables. From the results of the optimization, it has been observed that the laminated glass difficult to break in the case that the tensile strength was high and that the adhesive strength was a little light. The penetration performance of an optimized laminated glass plate was noticeably better in comparison with a commercial laminated glass plate.

Abstract: A new enhanced Discontinuous Deformation Analysis method (EDDA) in conjunction with Natural Neighbor Interpolative (NNI) bases for modeling the system composed of high order deformable solids is developed. The advantages of NNI lie in its efficiency and the interpolative property when employed as the shape functions. The anchor reinforcement algorithm is also implemented in the EDDA for modeling high order deformable solids. The numerical results of simple problems by using the proposed method agree well with the corresponding analytical results, and certain slope reinforcement problems are also simulated with rational numerical results, which verify efficiency and accuracy of the EDDA.

Abstract: This document explores the possibility of the discrete element method (DEM) being applied in nonlinear dynamic analysis of space frame structures. The method models the analyzed object to be composed by finite particles and the Newton’s second law is applied to describe each particle’s motion. The parallel-bond model is adopted during the calculation of internal force and moment arising from the deformation. The procedure of analysis is vastly simple, accurate and versatile. Numerical examples are given to demonstrate the accuracy and applicability of this method in handling the large deflection and dynamic behaviour of space frame structures. Besides, the method does not need to form stiffness matrix or iterations, so it is more advantageous than traditional nonlinear finite element method.

Abstract: Discrete Element Method (DEM) computer simulation is used to examine the influence of contact force between two-dimensional aggregates of polystyrene microsphere formed on the air-liquid interface. Colloidal aggregates have been treated as the granular material or discontinuum materials. The interaction force models are related to experiment which had done by digital video microscopy. The interaction mechanisms of the contact forces between particles in the colloidal system can be considered as a combination of spring and dashpot force and van der Waals force. According to the DEM, the interaction forces are evaluated to introduce relations between particles and the result comparison between the computer simulation and the experimental work. This study indicates that the behavior of the colloidal aggregates depends on the long-ranged (spring and dashpot) and the short-ranged interaction force (van der Waals). Besides, the behaviors shown in both computer simulation and the experiment are in good agreement. Thus, this computer simulation method can mimic the behavior of colloidal aggregates forming as a monolayer at the air-liquid interface.