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Typical structures of inverse opal photonic crystals after ALD infiltration and template burn-out showing the hollow-shell structures (a) top view (b) cross section (inset) top-view of an ion-milled section. The red markers show typical interstitial sites for ALD-based photonic structures. Former PS template particles' size are 1.5 and 0.7 µm for (a) and (b), respectively. Scale bars are 3 microns and 500 nm at the inset.
Source publication
Discrete Element Method (DEM) has been used for numerical investigation of sintering-induced structural deformations occurring in inverse opal photonic structures. The influence of the initial arrangement of template particles on the stability of highly porous inverse opal α-Al2O3 structures has been analyzed. The material transport, densification,...
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Citations
... This expression was directly used by Henrich et al. [25] in the DEM context. Dosta et al. [26] have recently shown that this model can result in very efficiently numerical implementations taking advantage of superior performance of the modern CUDA-based codes [27]. ...
A novel discrete element method-based approach for modeling of solid state sintering of spherical metallic powder is presented. It tackles the interplay between the thermodynamical mass transport effects arising in the vicinity of the grain boundary between the particles and their mechanical interaction. To deal with the former, an elementary model is used that describes the behavior of the matter flow at the grain boundary such that neck growth and shrinkage are properly captured. The model solves a set of partial differential equations which drive the changes of the corresponding geometry parameters. Their evolution is transformed into the equivalent normal sintering force arising in each sinter neck. To capture the mechanical interaction of particles due to their rearrangement resulting from the geometry changes of each individual contact, the entire assembly is modeled as an assembly of 2-nodal structural elements with 6 degrees of freedom per node. The stiffness properties are estimated employing the approximations from the bonded DEM. The numerical implementation then constitutes a two-step staggered solution scheme, where these models are applied sequentially. The performed benchmarks reveal the plausibility of the proposed approach and exhibit good agreement of both neck growth and shrinkage rates obtained in the numerical simulations with the experimental data.
... Numerical approaches have played a crucial role in elucidating thermomechanical phenomena, contributing to the control and optimization of the materials processing chain. Namely, the finite element method (FEM), the finite volume method (FVM) and the discrete element method (DEM) have been applied to model thermal phenomena in fluidized and packed beds [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] as well as for modeling of isothermal sintering [32][33][34][35][36][37][38]. Nevertheless, scarce numerical studies on fast-firing, based on FEM and FVM essentially, are found in the literature [4,36,39]. ...
... Many DEM-based studies of sintering processes were performed using the model proposed by Parhami & McMeeking [42] for free and pressure-assisted isothermal sintering. This model has been extensively applied to model particles [35,40,[43][44][45] and pores [33,34] rearrangement, anisotropic [46,47] and constrained [38,48] sintering, as well as the evolution of heterogeneities/defects during sintering. The Parhami & McMeeking model [42] was extended to describe grain coarsening [43,49], to consider variable coordination numbers [37], and to model the elastic component of sintering besides viscous flow [50][51][52]. ...
... The simulation framework MUSEN [54] was used to perform the simulations, an open-source software widely used in DEM investigations [32][33][34]41,55,56]. This system supports parallel computing on GPU based on the CUDA platform, which significantly reduces computation time, thus efficiently simulating millions of discrete objects [34,54]. ...
An original discrete element model for coupling thermo-mechanics with sintering is presented to disclose the thermo-micromechanical behavior of particulate systems and their densification process under rapid firing. The paper focuses on the numerical model formulation and application on the fast-firing of Al2O3, including its verification with literature. Particular emphasis is given to the evolution of thermal and densification gradients over sintering conditions and sample length, focusing on the microstructure evolution, shrinkage and the characteristic densification phenomena. Relationships between defects, microstructure, and sintering parameters are further analyzed. The numerical results present good agreement with the thermal behavior of fast-sintered Al2O3. Finally, the time-dependent change of material microstructure concerning coordination number evolution, cohesive neck size distribution, gradients of temperature, and sample length are explored.
... Furthermore, due to the discrete nature and non-uniform positioning of primary particles, there are still no effective strategies to run BPM simulations with periodic conditions. To compensate for the high computational effort of mesh-free BPM method, parallelization for graphics processing units can be applied [16] . ...
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... Eqs. (16) and (17) ) were varied and their influence on force-displacement characteristic was analyzed. Based on the deviations between experimental data and simulation results and using iterative Newton's optimization approach, an optimal parameter set was identified. ...
The application of mesh-free discrete element method (DEM) for modeling of macroporous inverse opals is proposed. The developed and implemented DEM-based strategy is applied to analyze stiffness and strength of inverse opals made of pure silica and inverse opals coated with titania layers of various thicknesses. Also, the influence of the porosity of the initial packing on the properties of the material is investigated. Simulation results have shown that due to the heterogeneous macroscopic structure and unequal material distribution in nodes, struts or near interstitial pores, strong inhomogeneities of the stress distribution arise. Spots of localized stresses located near the interpore openings are the sources of initial defects and small interpore cracks. Reducing the overall porosity or an additional coating of the structure with a titania layer allows to partially homogenize and improve its mechanical properties.
It was shown that the obtained simulation results are in very good agreement with previous studies. Despite large computational effort, the performed analysis confirms the high efficiency of the proposed DEM-based approach and demonstrates its great potential for use in problems of a similar class: for modelling of complex-structured multicomponent materials.
... However, the development of a sintering model for porcelain tiles including these aspects is beyond the scope of this work. It is envisioned that a microscale calculations approach like the discrete element method can allow to include these aspects [59,12]. ...
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... Generally, the DEM was introduced for modeling granular materials in the pioneering works by Cundall [24,25] and Walton [26]. Recently, special DEM models are developed for powder metallurgy processes [27][28][29][30][31][32][33][34][35]. Most of the DEM applications for powder metallurgy have considered one-phase powder; there are very few works dealing with two-phase powders [36][37][38][39]. ...
In this paper, the discrete element method framework is employed to determine and analyze the stresses induced during and after the powder metallurgy process of particle-reinforced composite. Applied mechanical loading and the differences in the thermal expansion coefficients of metal/intermetallic matrix and ceramic reinforcing particles during cooling produce the complex state of stresses in and between the particles, leading to the occurrence of material defects, such as cracks, and in consequence the composite degradation. Therefore, the viscoelastic model of pressure-assisted sintering of a two-phase powder mixture is applied in order to study the stress field of particle assembly of intermetallic-ceramic composite NiAl/Al2O3. The stress evaluation is performed at two levels: macroscopic and microscopic. Macroscopic averaged stress is determined using the homogenization method using the representative volume element. Microscopic stresses are calculated both in the body of particles and in the contact interface (necks) between particles. Obtained results are in line with the cooling mechanism of the two-phase materials.
... Dosta). a wide spectrum of tasks starting with classical problems related to modelling mechanical behaviour (Zhu et al. 2008 [1]), ending with the advanced applications like simulating sintering processes (Besler et al. 2016 [2]; Dosta et al. 2020 [3]). Discrete element method implies calculating the motion of a large number of small objects (most often spherical particles) by computing Newton's equations for each of them. ...
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