Packing Structure Of Particles Research Articles

Premelting Theory‐Based Mechanism for Water Freezing in Saline Soil

AbstractThe unfrozen water content constitutes a pivotal parameter in freezing soil, significantly impacting its thermal‐mechanical and deformation behavior. This study delves into the alterations in soil attributes as unfrozen water content varies. It examines the influences of impurities, van der Waals forces, and Coulomb forces on the water film, employing the premelting theory as a foundation. A critical state curve quantifying the ratio of the surface charge density to impurity concentration is parameterized for various soil types. Subsequently, combining the theory of effective solution concentration, we have provided calculation methods for the particle surface parameters of pore solutions as ideal and non‐ideal dilute solutions, respectively. This has determined the key variables in the model. Additionally, through the integration of equivalent particle sizes, packing structure, and water film thickness, a calculation model is devised and verified for determining the unfrozen water content and residual water content within in freezing soil. The findings indicate that fluctuation in the unfrozen water content primarily stem from impurities. In soils with equivalent saline content, impurity levels exhibit proportionality to the equivalent particle sizes. The residual unfrozen water is predominantly present within the absorbed water layer.

Mesoscale mechanical models for active materials in lithium-ion batteries using the multi-particle finite element method

The stability and mechanical integrity of electrode active materials have a significant impact on the safety and performance of lithium-ion batteries (LIBs). The study of mechanical properties of active materials is crucial for the safety design of batteries. Researchers have conducted several models for describing the mechanical behavior of active materials. However, an accurate mechanical model that can reflect the packing structure of active particles and achieve the multiscale mechanical analysis of active materials is still lacking. To bridge this gap, a three-dimensional (3D) mesoscopic model based on the multi-particle finite element method (MPFEM) is proposed in the present study. The numerical simulation results show that the established model is in good agreement with the experimental results for the description of the compression behavior of the active material. Based on the model, the effects of various factors on the mechanical behavior of the active materials are analyzed. The results deepen the understanding of the multiscale mechanical behavior of anode active materials and provide fundamental insights for the future development of safety design for LIBs.

Numerical investigation on the densification of granulated porous indium tin oxide powders before compaction

Dense and uniform initial packing structures of powders are of key significance in powder metallurgy process, which can provide the precondition for the fabrication of high-performance components with low cost and high efficiency. In this paper, the packing densification of indium tin oxide (ITO) granulated micro powders with continuous size distributions and internal porosity under three-dimensional vibrations was numerically investigated by discrete element method (DEM). Firstly, the DEM model was validated by physical experiments, and the contact parameters between particles and the porosity therein were determined. Then the effects of operating parameters on the macro/micro properties (e.g., packing density, coordination number (CN), pores, and forces) of the packing structures were analyzed. Results show that the mean CN cannot intuitively reflect the packing structure due to the complex and varied inter-particle contacts caused by the inhomogeneity of the particle size in a multi-sized granular system. Additionally, the excellent packing structure of porous ITO particles is always obtained from low amplitude when the vibration intensity is the same. Corresponding mechanism analyses reveal that higher amplitude normally causes strong convective diffusion, leading to more pores in the packing. This increases the probability of wedging effect occurring during settling, thereby reducing the packing density. However, optimal packing quality with low amplitude can only be achieved when coupled with high frequency. Therefore, applying vibration is an effective way to achieve dense packing of porous spherical particles, especially at low amplitude and high-frequency operating conditions.

Porous-media model based particle-resolved simulation of a fixed bed with olefin catalytic cracking reaction

Understanding the interstitial reacting flow in particle packing structure and its relation with the reaction performance is crucial to designing a highly efficient fixed bed reactor. This study uses a particle-resolved approach with a porous-media model-based immersed boundary method to simulate an olefin catalytic cracking (OCC) fixed bed with 150 cylindrical particles by combining a six-lump kinetic model and mass transfer model. The effects of weight hourly space velocity (WHSV) and particle shape are further investigated in analyzing conversion, concentration variation, flow structure and pressure drop. The study reveals a three-stage pattern in variation of product concentration along the packing structure height with different WHSVs, providing the basis for determining the optimal packing height. It also finds that the hollow-cylindrical particle manifests the best reaction performance while the cylindrical particle the worst. The coordination of surface area and pressure drop of the packing structure determines the OCC reaction effectiveness.

Mechanical grinding kinetics and particle packing novel characterization of iron ore tailings as inert filler for cement mortar

This study utilized image processing techniques to extract the morphological parameters of IOTs and established a grinding kinetic equation for particle morphology. The Divas-Aliavden equation and RRB model were applied to analyze the grinding kinetics of particle physical parameters. The Fuller and MAA particle packing models were employed to discuss the packing structure and density of particles in mortar. The relationship between particle physical parameters and compressive strength in the IOTs-cement system was explored through path analysis and grey correlation analysis. The results indicated that as the grinding process of IOTs progressed, the particle fineness decreased, the uniformity of particle size distribution and roundness increased, and using IOTs as inert fillers in mortar improved the particle packing structure and increased system density. Path analysis revealed the key influence of particle roundness on compressive strength, while the grey correlation analysis revealed that particles in the 2–60 μm range exerted a positive impact on the compressive strength of the composite binder system, with the most pronounced effect observed within the 8–16 μm range. Based on economic and technical considerations, the optimal mechanical grinding time for IOTs used as inert filler in cement mortar was determined to be 2.5 h.

A spheropolyhedral-based discrete element lattice Boltzmann method for simulation of non-spherical adhesive particulate flow

Non-spherical particulate flow is commonly encountered in nature, industry and our daily life. But up to now, there still lack effective model to describe the adhesive elastic collision between non-spherical microparticles. To solve this problem, a spheropolyhedral-based discrete element method (DEM) combined with Johnson-Kendall-Roberts (JKR) model is proposed. The contact between non-spherical particles is attributed to the contacts between three geometry features, including vertice-vertice (V-V), vertice-edge(V-E), vertice-face (V-F) and edge-edge (E-E). The JKR adhesive model is modified to calculate the contact force of the contacting geometry features based on the actual contact area. Meanwhile, the lattice Boltzmann coupled with the immersed moving boundary (LB-IMB) method is employed to simulate the fluid flow and fluid-particle interaction. The novel spheropolyhedral-based DE-LBM is verified to be accurate and effective by several experiments and the data in references. Finally, an application test for simulating the packing process of non-spherical microparticles is presented. The method well predicts the packing structure of both adhesive and non-adhesive non-spherical particles, meaning that it can be easily extended to simulate the massive non-spherical microparticles with high effectiveness and efficiency. Program summaryProgram Title: adhesive contact force model for non-spherical particleCPC Library link to program files:https://doi.org/10.17632/vswvv7ppz2.1Developer's repository link:https://github.com/QIAN-C/adhesive-force-model-for-non-sphericalLicensing provisions: GNU General Public License v3Programming language: C++Nature of problem: Various methods have been proposed to handle the complex shapes of non-spherical particles in the discrete element method. However, there is still a lack of effective models for calculating the contact force between the non-spherical fine particles, particularly the adhesive forces.Solution method: Based on the sphere-polygon algorithm and the JKR model, this program has developed a contact force model that can accurately calculate adhesive forces between non-spherical fine particles within the framework of the open source library MechSys (URL: http://mechsys.nongnu.org/index.shtml).

Effect of particle packing structure on the elastic modulus of wet powder compacts analyzed by persistent homology

This study applies persistent homology (PH) to the structural analysis of wet powder compacts to clarify the effect of packing structure on the elastic modulus, and proposes an equation for the relationship between saturation and elastic modulus based on the index of structural homogeneity. The relationship between the saturation and the elastic modulus was experimentally obtained by compression tests of wet powder compacts. The elastic modulus decreased linearly with increasing saturation, but the slope was different depending on the packing structure of compacts which were made from high purity alumina with different particle size distributions. PH was applied to the packing structure of particles of different diameters calculated by DEM simulation to evaluate the packing structure. The features of each packing structure were extracted by PH, and the index of structural homogeneity was obtained. A new empirical equation is proposed which can predict the relationship between the elastic modulus and the saturation considering structural homogeneity, specific surface area, surface tension, and porosity as the main factors affecting the elastic modulus in the partially saturated state. These results indicate that PH analysis is effective to evaluate the packing structure and that this method may predict the mechanical properties of wet powder compacts.

Study on the stability of particle packing structure based on cells

The macroscopic mechanical property and the stability of granular mechanics system are determined by packing structure. Cells play a fundamental role in granular statistical mechanics and thus cells were utilized in this paper to research the packing structure of disk particles and gear particles in a two-dimensional cubic container. The probability distribution of cell order satisfies the exponential function distribution and is independent of intergranular friction, the size of system and vibration. Furthermore, it is observed that friction and system size are the key factors affecting the stability of particle packing structure. Significantly, the relationship between volume fraction and packing structure of disk particles is established under vibration. The experimental results reveal the characteristics of ordered packing structure of disordered particle system in mesoscale and provide data reference for perfecting the theory of particle mechanics.

Reliability study of super-ellipsoid DEM in representing the packing structure of blast furnace

In industrial blast furnaces (BFs), the investigations involving the flow behaviors of particles and the resultant burden structure are essential to optimize its operation stability and energy consumption. With the advance of computing capability and mathematical model, the discrete element method (DEM) specialized in characterizing particle behavior has manifested its power in the investigation of BFs. In the framework of DEM, many particle models have been developed, but which model is more suitable for simulating the particle behaviors of BFs remains a question because real particles in BFs have large shape and size dispersity. Among these particle models, the super-ellipsoid model possesses the ability to change shape flexibly. Therefore, the focus of this study is to investigate whether the super-ellipsoid model can meet the requirement of authenticity and accuracy in simulating the behaviors of particles with large shape and size dispersity. To answer this question, a simplified BF charging system composed of a hopper and a storage bin is established. The charging process and the final packing structure are analyzed and compared between experiments and simulations with different shape indexes. The results show that super-ellipsoid particles have prominent advantages over spherical particles in terms of representing the real BF particles, and it can more reasonably reproduce the flow behaviors and packing structure of experimental particles. The computation cost of super-ellipsoid particles is also acceptable for engineering applications. Finally, the micro-scale characteristics of packing structure is analyzed and the single-ring charging process in industry-scale BF using super-ellipsoid particles is conducted.

Anisotropic microstructural evolution and coarsening in free sintering and constrained sintering of metal film by using FIB-SEM tomography

The anisotropic microstructure develops during powder processing and constrained sintering. FIB-SEM tomography was used to investigate the microstructural evolutions of Au submicron particles during free sintering and constrained sintering. The decrease in total surface area and the coarsening, i.e. the increase of mean intercept length of solid phase, were observed during the densification process. The anisotropic packing structure of spherical particles induced by casting process was characterized by area weighted fabric tensor, which represented the bond orientation and the anisotropy of contact area. In free sintering, the initial anisotropy in packing structure decreased with densification. In constrained sintering, the initial anisotropy observed by the mean intercept length of pore was reversed in the later stage. The microstructure evolved so as to form the elongated pores along the thickness direction. An open pore structure model was presented to explain the microstructural evolution in the intermediate stage.

Anisotropic Microstructural Evolution and Coarsening in Free Sintering and Constrained Sintering of Metal Film by Using FIB-SEM Tomography

The anisotropic microstructure develops during powder processing and constrained sintering. In the present study, the microstructural evolutions of Au submicron particles during free sintering and constrained sintering were investigated by FIB-SEM tomography. The decrease in total surface area and the coarsening, i.e. the increase of mean intercept length of solid phase, were observed during the densification process. The anisotropic packing structure of spherical particles induced by casting process was characterized by area weighted fabric tensor, which represented the bond orientation and the anisotropy in contact area. In free sintering, the initial anisotropy in packing structure decreased with densification as indicated by the decrease in deviatoric component of surface energy tensor. In constrained sintering, the initial anisotropy observed by the mean intercept length of pore was reversed in the later stage. The microstructure evolved so as to form the elongated pores along the thickness direction.

Evaluation of Mechanical Properties of Composite Solid Propellant by Genetic Engineering of Materials: Part B: Modeling of Minimum Representative Unit for Multi‐Modal Particle Packing Structure Based on Formulation of Composite Solid Propellant

AbstractTo show the actual particle packing structure of AP/Al/HTPB propellant with multi‐modal fillers, a minimum representative unit of particle packing structure is established. In the minimum representative unit, the particle size of fillers in each mode is identical to the value in the propellant formulation. Meanwhile, on the basis of the amount series of fillers in the per unit propellant, the amount of fillers in each mode is respectively divided by that of the fewest filler, thus the amount series of fillers in the minimum representative unit is obtained. Further, with the condition that the average density of the unit is the same as that of the propellant, the side length of the minimum representative unit could be uniquely determined. In order to generate the particle packing structure with particles evenly distributed in the unit, a two‐step algorithm is put forward. In the first step, the genetic algorithm is adopted to search for an evenly and non‐overlapping distribution for the few and coarser particles. In the second step, the residual finer particles are randomly placed in the voids among the coarser particles by a modified L−S algorithm. Results showed that the particles are distributed more evenly in the packs generated by the two‐step algorithm than in packs generated by the classic L−S algorithm.

Self-compacting concrete with TPP fly ash

The prospects and problems of multilevel optimization of the dispersed composition of self-compacting concrete are considered with the aim of significantly increasing its construction and technical properties, with a minimum content of binder. Theoretical and practical principles have been developed for the design of disperse-particle size distribution of self-compacting concrete mixtures for high-strength concrete, in which various types of dispersed mineral modifiers (MM) are used, including fly ash of thermal power plants (TPPs). Effective MMs for self-compacting concrete mixtures are varied granular blast furnace slag and fly ash of thermal power plants, which create a dense packing structure of particles of a multicomponent binder with a low degree of disorder and ensure a decrease in the consumption of Portland cement in concrete by 43-48%. With such a choice of the type and parameters of MM, self-compacting concrete mixtures are characterized by lower water content, high viscosity and a low level of ultimate shear stress, ensuring its high-quality compaction. To study the properties and structure of concrete, quartz sand with Mk −2.58 and granite crushed stone were used as a fine aggregate. 5-10 and 10-20mm, Portland cement of class CEM I 52.5N, finely dispersed blast furnace granulated slag, fly ash of thermal power plants. and Glenium 430 superplasticizer. Research methods: the shape and size of the dispersed particles of the components were determined by a laser analyzer, the mobility of the concrete mix according to GOST 10181-2014, the compressive strength of concrete according to GOST 10180-2012. The structure of the cement stone was studied by thermographic and x-ray phase analysis methods. The strength of concrete only from the use of fly ash from TPPs instead of the equivalent part of fine aggregate increases by 4.1−9.2%.

Experimental study on 3D vibrated packing densification of mono-sized dodecahedral particles

Packing densification of mono-sized regular dodecahedral particles subjected to 3D vibrations was studied through systematical physical experiments. The influences of various vibration conditions and container size on the packing density were analyzed and the operating parameters were optimized. The obtained microstructures of different packings were characterized through 3D CT non-destructive inspection. The results show that by properly controlling the vibration conditions, the transition from initial loose to final dense packing structure of mono-sized regular dodecahedral particles can be reproduced. A maximum packing density of 0.709, which is the currently obtainable densest random packing structure of mono-sized regular dodecahedral particles in physical experiments, can be realized by extrapolating the packing densities obtained in different sized containers. Microscopic analyses on the 3D computer re-constructed packing structures from experiments clearly demonstrate the specific characteristics of the generated initial loose and final dense packings. The obtained results can enhance the deep understanding of packing behavior of dodecahedral particles and provide researchers with valuable reference to the design and fabrication of some new materials.

МНОГОКОМПОНЕНТНОСТЬ – ОСНОВНОЙ ФАКТОР ФОРМИРОВАНИЯ СТРУКТУРЫ И СВОЙСТВ ВЫСОКОПРОЧНЫХ БЕТОНОВ

The prospects and problems of multicomponent multilevel optimization of the dispersed composition of self-compacting concrete are considered with the aim of significantly increasing its construction and technical properties, with a minimum content of binder. Theoretical and practical principles have been developed for the design of disperse-particle size distribution of self-compacting concrete mixtures for high-strength concrete, in which various types of dispersed mineral modifiers (MM) are used, including fly ash of thermal power plants. Effective MMs for self-compacting concrete mixtures are differently dispersed granular blast furnace slag, fly ash of thermal power plants and silica fume, which create a dense packing structure of particles of a multicomponent binder with a low degree of disorder and ensure a decrease in the consumption of Portland cement in concrete up to 50% and higher. With such a choice of the type and parameters of MM, self-compacting concrete mixtures are characterized by lower water content, high viscosity and a low level of ultimate shear stress, ensuring its high-quality compaction. To study the properties and structure of concrete, quartz sand with Mk -2.58, granite crushed stone fr. 5-10 mm, Portland cement of class CEM I 52.5 N, finely dispersed granulated blast furnace slag, fly ash of thermal power plants, micro-silica and superplasticizer Glenium 430. For a uniform course of the pozzolanic reaction, a finely dispersed cement fraction was used in each micro-volume. Research methods: the shape and size of the dispersed particles of the components were determined by a laser analyzer, the mobility of the concrete mix in accordance with GOST 10181-2014, the compressive strength of concrete in accordance with GOST 10180-2012. The structure of the cement stone was studied by thermographic and X-ray phase analysis methods.

3d tomography analysis of the packing structure of spherical particles in slender prismatic containers

Abstract In granular media, topological features are known to determine the effective material properties and boundary behavior when interacting with other structural components. X-ray computed tomography results are reported on sphere packing structures in slender prismatic containers (X = 20, Y = Z = 80 mm), filled and vibrated with both monosized spheres (diameter d = 2.4 mm), Exp. (M), and polydisperse spheres (1 mm < d < 1.25 mm), Exp. (P). Packing structures were characterized by void fraction distributions, coordination numbers, contact angle distributions and Voronoi packing fractions. In (M), an almost perfect hexagonal dense packing exists in the total volume, associated with a packing fraction γ t≈0.68. In additional packing experiments, large γ t values were achieved as well. Although the d spread in (P) is relatively small, significantly different results are obtained: γ t≈0.62, regular structures are restricted to narrow wall zones and distributions in the container volume are nonhomogeneous. It is argued that the small degree of ordered structure is a characteristic feature of polydispersity for efficiently vibrated sphere packings.

Tape casting and characterization of yttrium iron garnet ferrite thick film for microwave substrate application

In this study, the tape casting and characterization of a yttrium iron garnet (YIG) ferrite thick film was carried out for microwave substrate applications. A high-performance YIG ferrite thick film was developed using a well-dispersed non-aqueous YIG slurry. The resulting green YIG film exhibited a smooth surface and a uniform particle-packing structure with a green density of 3.12 g/cm3. The YIG substrate sintered at 1480 °C exhibited a dense microstructure and good properties with a bulk density of 5.06 g/cm3, dielectric constant (εr) of 14.2, dielectric loss (tanδe) of 1.8 × 10−4 (10 GHz), saturate magnetization (4πMs) of 168.2 mT, coercive force (Hc) of 0.47 Oe, and ferromagnetic resonance linewidth (ΔH) of 5.2 KA/m. Thus, the YIG casting film developed in this study was found to be suitable for microwave substrate applications.

In Situ X-ray Tomography and 3D X-ray Diffraction Measurements of Cemented Granular Materials

In situ x-ray tomography and three-dimensional (3D) x-ray diffraction analysis have been combined to investigate the mechanical behavior of noncemented and lightly cemented quartz particles under quasistatic confined uniaxial compaction. The motivation for this study is to understand the particle-scale origin of the mechanical behavior of cemented particulate materials and to isolate what makes this behavior distinct from that of noncemented particulate materials. Tomography measurements elucidated the particle packing structure, contact fabric, cementation, and particle fragmentation, while 3D x-ray diffraction measurements provided insight into particle rotations and particle-resolved strain and stress tensors. The cemented sample was found to exhibit higher resistance to individual particle fragmentation and significantly restrained particle motion, compared with the noncemented sample, likely due to the cement bridges between particles. This reduction in particle fragmentation and motion may explain the significantly enhanced macroscopic stiffness of the cemented sample, as well as the strong alignment of intraparticle principal stresses with the macroscopic strain direction. These findings advance particle-scale understanding of cemented granular media and provide motivation for further research focused on developing fundamental understanding of the constitutive response of these materials.

Graded evolution of anisotropic microstructure during sintering from crystal‐oriented powder compact

AbstractAnisotropic sintering, including shrinkage and grain growth, was examined for c‐axis‐oriented (Sr,Ca)2NaNb5O15 (SCNN) ceramics, which were prepared by colloidal processing under a magnetic field. In the c‐axis‐oriented SCNN powder compact, shrinkage and grain growth along the c‐axis were higher than those along the a‐axis. The anisotropic microstructural development was clearly associated with anisotropic sintering shrinkage. X‐ray diffraction, scanning electron microscopy, and energy back scattering diffraction showed that the grain growth of oriented particles by including random grains contribute to the development of the oriented microstructure. Finally, the highly crystal‐oriented SCNN ceramics with a densified microstructure were obtained through anisotropic sintering. These results clearly showed the potential to develop a well‐defined anisotropic microstructure during sintering by designing and controlling the particle packing structure in a powder compact.

Packing structure analysis of flexible rod particles in terms of aspect ratio, bending stiffness, and surface energy

In powder packing, it is essential to understand the packing structure of different powders. In this study, we numerically analyzed the packing structure of flexible rod particles using a discrete element method. We quantitatively evaluated the packing structure using the aspect ratio, flexibility, and surface energy of the flexible rod particles and determined the effects of these factors on the packing structure in terms of the radial distribution function, coordination number, and porosity. The flexible rod particles used for powder packing were simulated using a worm-like chain model, in which multiple spherical particles were connected in the form of a rod. The surface energy acting on the particles was represented using the Johnson–Kendall–Roberts model. The packing structure of the particles was quantitatively analyzed by filling a cylindrical container with the particles. The aforementioned factors affected the packing structure to different extents depending on the conditions. When the aspect ratio of the particles was high, the flexibility significantly affected the packing structure. However, when the aspect ratio of the particles was low, the effect of the surface energy was predominant.