Packing Arrangement Of Particles Research Articles

Investigation on instability modes of sand under biaxial shearing accounting various specimen generation techniques in DEM

Instabilities in granular material usually initiate at the microscale due to the presence of internal heterogeneity arising from variation in the particle packing arrangement. The present work elucidates the effect of various specimen generation techniques adopted in DEM on the initial sample heterogeneity and its subsequent influence on the instability response of sand under biaxial shearing. Dense and loose specimens are prepared using five different specimen generation techniques and homogeneity within the specimens has been analyzed in terms of spatial variation of porosity, anisotropy in the contact force and fabric structure. The initiation and subsequent evolution of different instability modes during shearing have been examined based on the spatial porosity distribution, relative particle displacement and particle rotation. Localized instability mode has been observed to emerge in dense specimens in form of cross-type shear bands with varying inclination and thickness for these different specimen generation techniques. Porosity and particle rotation based instability prediction indicate a delayed onset of shear band in comparison to identifications from relative particle displacement and bifurcation of local strains. The loose specimen exhibits bulging type diffused instability accompanied by large relative particle displacement and rotation scattered across the specimen.

A Proposed Mix Design of Concrete with Supplementary Cementitious Materials by Packing Density Method

Various mix design methods have been proposed by different researchers for determining the quantities of concrete ingredients, using local materials and to achieve required strength and durability. It is always desirable to compose the aggregates as dense as possible when selecting a concrete mix design. Hence packing density is one of the most important parameters which minimize the necessary amount of binder, result in less shrinkage and creep. In this research, a mix design method is proposed by using the principle of dense particle packing arrangement to sustainable concrete by partial replacement of cement and sand with fly ash and pond ash, respectively. Various mixes were prepared with combinations of replacement material, and a best combination is selected according to maximum compressive strength of 28-day curing. That optimized combination is further designed by packing density method and compared the mix proportions with Indian Standard Code method. It is concluded that packing density method reduces the material consumption as well as cost of construction with keeping the environment clean and green without compromising the strength and durability.

Effects of particle distribution of matrix on microstructure and slag resistance of lightweight Al2O3–MgO castables

For lightweight castables containing microporous aggregates, the compacted matrix component is a key factor in determining their useable lifespan, and this matrix is influenced by both the particle packing and sintering process. In this study, the grain grading of lightweight Al2O3–MgO castable matrices was adjusted to create a particle size distribution that close to the Andreassen model with q-values of 0.25, 0.28, 0.31, and 0.34. After sintering at 1500°C for 3h, the microstructures and slag resistances of lightweight Al2O3–MgO castables with different particle packing arrangements were compared and discussed. The results show that a q-value no higher than 0.31 was needed to ensure formation of a denser matrix. For the smallest q-value that was studied (0.25), the resulting matrix had a large grain size (5–12µm) and a relatively small average pore size (D50=2.10µm), which favours the formation of Ca (Al, Fe, Mn)12O19 layer distributed within the matrix. This resulted in the highest resistance to slag corrosion observed (Ic=7.93%), whereas the cracks existing between the matrix and the aggregates due to a large volume shrinkage decreased the slag penetration resistance (Ip=45.9%). The microstructure of the matrix with a q-value of 0.28 was uniform and compacted, which reached an acceptable compromise between resistance to slag corrosion (Ic=22.4%) and resistance to slag penetration (Ip=11.5%).

Binder distribution model for asphalt mixtures based on packing of the primary structure

Film thickness describes the coating around aggregate particles on asphalt mixtures. The standard method of calculating film thickness has proven to present several limitations, such as assuming an average thickness independent of particle size, being completely independent to the porosity of the mixture and considering only one mineral type. In this paper, a binder distribution model is developed for aggregates according to size and role in the structure. The aggregates are separated into two different structures: primary structure, the load bearing one, and secondary structure, smaller material that provides stability to the skeleton. A coating thickness for these two structures is calculated from a geometrical consideration that includes the packing arrangement of particles and the effect of overlapping as the film grows. The results were compared with known rutting performance of field mixtures and moisture conditioned laboratory mixtures, showing a good correlation between film thickness and resistance to failure.

In Situ Environmental Scanning Electron Microscope Observations of Colloidal Failure Mechanisms Using the Brazilian Disk Test

This paper presents data produced using a novel test fixture to study the crack initiation and fracture mechanisms in brittle colloidal systems, in situ in an Environmental Scanning Electron Microscope (ESEM), based on the Brazilian disk test. The test is based on diametral compression loading of a disk of material, which causes a tensile stress in the centre of the disk perpendicular to the loading direction. Key advantages over commercial tensile tests are simplicity of specimen preparation, especially important for fragile and brittle materials, which because of their nature in many cases cannot be microscopically characterised after testing. The test was successful in creating the desired perpendicular tensile stresses and yielded diametral cracks across the latex specimens. It was found that when end crushing was minimal, multiple cracks initiated at several points on the disk and a number of factors appeared to influence the propagation of cracks through the latex, these include: particle packing arrangements, surface defects, and the presence of other cracks. Following the onset of fracture, it was observed that the cracks connected to form a single failure route, here described as the path of least resistance. This, in essence, resulted in the crack taking a route around stronger, more ordered regions of the latex (be they “crystals” or surface defects). The experimental results presented and discussed here represent the first attempt to utilise this loading arrangement in the study of crack propagation in colloidal systems.

The effect of forming stresses on the sintering of ultra-fine Ce0.9Gd0.1O2−δ powders

Abstract The effect of particle and pore arrangement on sintering and densification of ultra-fine (∼130 nm) Ce0.9Gd0.1O2−δ powder was evaluated. The common understanding that higher initial density of a ceramic network leads to a higher sintered density is not valid for fine powders, which have extremely good sinterability when there is a favourable particle packing. The effect of the applied stresses during forming (which produce different particle packing arrangements) was investigated by forging green bodies by different shaping techniques, including casting, and cold isostatic pressing. Samples formed with techniques that apply low levels of stress had a particle arrangement which significantly enhanced sintering at low temperature, compared to those prepared by high stress techniques. The sample geometry, heat treatment for organic removal and the initial density of the green body had a negligible effect on the final density when the ratio of the pore size to particle size was around 1.

Estimating the Rate of Erosion of a Silty Sand Treated with Lignosulfonate

AbstractThis paper describes a theoretical model to capture the rate of erosion of a silty sand based on the principle of conservation of energy. Erosion is considered to begin when the interparticle bonds between grains are broken by hydrodynamic stresses exerted on the soil particles. These detached particles are then suspended and transported by the flow of eroding fluid. It is further assumed that once the particles are fully suspended and have reached the flow velocity, resettlement does not take place. Stabilization of soil particles because of lignosulfonate (LS) treatment is represented by the increased strain energy required to break the interparticle bonds. The equation proposed in this study is based on the shear stress-strain characteristics, mean flow velocity, mean particle diameter, and the packing arrangement of particles. The result of the proposed study is presented in the form of erosion rate versus the hydraulic shear stress. The model is validated with a series of laboratory erosion t...

Computer simulations of particle–bubble interactions and particle sliding using Discrete Element Method

Three dimensional Discrete Element Method (DEM) computer simulations have been carried out to analyse the kinetics of collision of multiple particles against a stationary bubble and the sliding of the particles over the bubble surface. This is the first time that a computational analysis of the sliding time and particle packing arrangements of multiple particles on the surface of a bubble has been carried out.The collision kinetics of monodisperse (33μm in radius) and polydisperse (12–33μm in radius) particle systems have been analysed in terms of the time taken by 10%, 50% and 100% of the particles to collide against the bubble. The dependencies of these collision times on the strength of hydrophobic interactions follow relationships close to power laws. However, minimal sensitivity of the collision times to particle size was found when linear and square relationships of the hydrophobic force with particles radius were considered.The sliding time for single particles has corroborated published theoretical expressions. Finally, a good qualitative comparison with experiments has been observed with respect to the particle packing at the bottom of the bubble after sliding demonstrating the usefulness of computer simulations in the studies of particle–bubble systems.

Laser sintering of blended Al‐Si powders

PurposeThe purpose of this paper is to study the effects of particle size distribution, component ratio, particle packing arrangement, and chemical constitution on the laser sintering behaviour of blended hypoeutectic Al‐Si powders.Design/methodology/approachA range of bimodal and trimodal powder blends were created through mixing Al‐12Si and pure aluminium powder. The powder blends were then processed using selective laser sintering to investigate the effect of alloy composition, powder particle size and bed density on densification and microstructural evolution.FindingsFor all of the powder blends the sintered density increases with the specific laser energy input until a saturation level is reached. Beyond this saturation level no further increase in sintered density is obtained for an increase in specific laser energy input. However, the peak density achieved for a given blend varied significantly with the chemical constitution of the alloy, peaking at approximately 9 wt% Si. The tap density of the raw powder mixture (assumed to be representative of bed density) was also a significant factor.Originality/valueThis is the first study to consider the usefulness of silicon as an alloying element in aluminium alloys to be processed by selective laser sintering. In addition the paper outlines the key factors in optimising processing parameters and powder properties in order to attain sound sinterability for direct laser sintered parts.

Effective Transport Properties of LiMn2O4 Electrode via Particle-Scale Modeling

The extension of Li-ion batteries, from portable electronics to hybrid and electric vehicles, is significant. Developing a better understanding of the role of material properties and manipulating the morphology of the particle clusters comprising Li-ion electrodes could lead to potential opportunities for attaining higher performance goals, for which the effect of both material properties and morphology needs to be considered in a physics-based model. In this work, different particle packing arrangements are analyzed for the calculation of effective transport properties and reaction density that appear in the porous-electrode formulation due to the volume-averaging process. Surrogate-based analysis is used to systematically construct and validate reduced-order models for species transport at the particle-electrolyte interface. The low effective solid transport predicted through microscale modeling indicates the effect of packing arrangement and tortuosity, an aspect not captured by the Bruggeman’s relation. Particle cluster simulations reveal a Li-ion flux quantitatively different than that predicted by the porous-electrode model due to the variation of overpotential at the microscale. The present study offers a first-step towards integration of the effect of microstructure into a macroscale simulation.

Froth touch samples viewed with Scanning Electron Microscopy

The stability of the thin films found in the froth phase of flotation plays an important role in the overall efficiency of the separation process. In turn, the physical behaviour of the particles attached to the films has a direct impact on the lamella stability. This effect is not fully understood. The film solids loading, or attached mass to area ratio, is an indicator of froth stability and has been measured by touch sampling of surface bubbles. Multiple samples can also be assayed as an indicator of maximum possible grade. Here the touch sample technique is used to show the particle packing arrangement on the film. This work presents images of touch samples from the top of the froth viewed under a Scanning Electron Microscope (SEM). Froth samples were obtained during batch flotation of glass beads with a size fraction of 90–150 μm. The packing arrangement of the particles attached to the surface lamellae were clearly resolved, making it possible to obtain a measure of film packing density using image analysis. These results can be used to validate and expand physical models that predict film stability.

An analytical model to study the effective stiffness of the composites with periodically distributed sphere particles

Abstract In order to analytically study the overall elastic stiffness of the composite containing periodically dispersed sphere particles, a new micro-mechanics model is developed in this paper. Three kinds of typical particle packing arrangements in the form of simple cubic lattice, body-centered cubic lattice and face-centered cubic lattice are considered and compared. The special characteristics of regular distribution are fully considered by incorporating the necessary geometrical symmetry conditions into strain Green’s function. It is found that particle arrangement obviously affects the macroscopic elastic response of such the kind of composite. Moreover, most of the predictions by the present model are in good agreement with the FEM computations. The effective Young’s modulus of BCC composite the effective shear modulus of SC composite are not in the range of the Hashin–Shtrikman bounds. The present model is also useful to verify some other numerical results mainly obtained by the unit-cell model, for instance, damage variables, matrix plasticity, etc.

Fabrication of yttria-stabilized-zirconia coatings using electrophoretic deposition: Effects of agglomerate size distribution on particle packing

Yttria-stabilized-zirconia (YSZ) particles with various size distributions have been electrophoretically deposited (EPD) on Fecralloy substrate to investigate the particle size effect on EPD coatings. The deposition rates, as-deposited particle packing densities, green densities and sintered (for 2 h at 1250 °C in air) coating hardnesses are dependent on particle size. The particle packing arrangement in EPD coatings can be affected by further electric field densification (EFD) of the as-deposited coating in which the wet EPD coating is immersed in pure solvent (acetylacetone) with the application of a constant electric field. The effect of EFD was found to be most effective on small particles (<0.5 μm) when they are co-deposited with large particles (>1 μm). The improvements are reflected in increased mechanical hardness of sintered coatings.

Simulation of non‐isothermal melt densification of polyethylene in rotational molding

AbstractRotational molding involves powder mixing, heating and melting of powder particles to form a homogeneous polymer melt, as well as cooling and solidification. The densification of a loose powder compact into a homogeneous melt occurs over a wide range of conditions as the material passes from a solid state into a melt state. The numerical simulation of the non‐isothermal melt densification in the rotational molding process is presented in this work. The simulation combines heat transfer, polymer sintering and bubble dissolution models, and is based on an idealized packing arrangement of powder particles. The predictions are in general agreement with experimental observations presented in the literature for the rotational molding of polyethylenes. The simulation allows for systematic and quantitative studies on the effect of molding conditions and material properties on the molding cycle and molded part density. Results indicate that the densification process is primarily affected by the powder characteristics, which are accounted for in terms of the particle size and the particle packing arrangement. The material rheological properties become increasingly important as the powder characteristics lessen in quality. The simulation demonstrated that while certain combinations of processing conditions help reduce the molding cycle, they have a detrimental effect on the densification process.

Variation of Packing Structure of Powder Compact with Particle Shape.

Material characteristics of powder compact are closely related to the packing arrangement of particles. In this paper, the effect of particle shape was investigated on the non-uniform packing structure. In the experiments, the shape of stainless steel particles was modified by changing the operational conditions of rotational impact blending and differently shaped particles were consolidated under piston press. The packing structure of the powder bed was expressed by void-size distribution. As a result, it has been clarified that the void-size distribution becomes narrow as the particle shape gets elongated, and the local voidage decreases. Thus, a uniform packing structure is apparently attained.

Effect of Particle Surface Roughness on Densification of Coarse‐Textured Soil

AbstractIt has been observed that soils on the Atlantic Coastal Plain compact to different bulk densities under the same compactive effort. It is hypothesized that densification differences observed among Ap horizon materials of these soils are partially due to variations in soil particle surface roughness. Surface roughness of Coastal Plain soil materials and sand size fractions derived from these materials were photographed and/or characterized by measuring the dense soil angle of response (DSAR) over a range of bulk densities. Altering the particle size distribution of a given material did not significantly influence the DSAR vs. Db (soil bulk density) relationship; the slopes and intercepts of these linear plots were not statistically different. However, plots of DSAR vs. Db for materials with different particle surface roughness had similar slopes, but different intercepts. It is proposed that the intercept of the DSAR vs. Db curve, or the value of DSAR at a given Db, be used to characterize soil particle roughness for coarse‐textured materials.It was further hypothesized that the DSAR at a given Db was directly related to particle packing arrangement stability, or resistance to further densification, of the soil material. To test this hypothesis, different levels of vibrational energy were applied to materials with different particle roughness but similar particle size distributions. Soil materials with the smoothest particles, i.e., those with the lowest DSAR at each Db, consistently produced the highest Db at each vibrational energy level.