Particle Shape Research Articles

Microstructural characterization of DEM-based random packings of monodisperse and polydisperse non-convex particles

Understanding of hard particles in morphologies and sizes on microstructures of particle random packings is of significance to evaluate physical and mechanical properties of many discrete media, such as granular materials, colloids, porous ceramics, active cells, and concrete. The majority of previous lines of research mainly dedicated microstructure analysis of convex particles, such as spheres, ellipsoids, spherocylinders, cylinders, and convex-polyhedra, whereas little is known about non-convex particles that are more close to practical discrete objects in nature. In this study, the non-convex morphology of a three-dimensional particle is devised by using a mathematical-controllable parameterized method, which contains two construction modes, namely, the uniformly distributed contraction centers and the randomly distributed contraction centers. Accordingly, three shape parameters are conceived to regulate the particle geometrical morphology from a perfect sphere to arbitrary non-convexities. Random packing models of hard non-convex particles with mono-/poly-dispersity in sizes are then established using the discrete element modeling Diverse microstructural indicators are utilized to characterize configurations of non-convex particle random packings. The compactness of non-convex particles in packings is characterized by the random close packing fraction fd and the corresponding average coordination number Z. In addition, four statistical descriptors, encompassing the radial distribution function g(r), two-point probability function S2(i)(r), lineal-path function L(i)(r), and cumulative pore size distribution function F(δ), are exploited to demonstrate the high-order microstructure information of non-convex particle random packings. The results demonstrate that the particle shape and size distribution have significant effects on Z and fd; the construction mode of the randomly distributed contraction centers can yield higher fd than that of the uniformly distributed contraction centers, in which the upper limit of fd approaches to 0.632 for monodisperse sphere packings. Moreover, non-convex particles of sizes following the famous Fuller distribution of the power-law distribution of the exponent q = 2.5, have the highest fd (≈0.761) with respect to other q. In contrast, the particle shapes have an almost negligible effect on the four statistical descriptors, but they are remarkably sensitive to particle packing fraction fp and size distribution. The results can provide sound guidance for custom-design of granular media by tailoring specific microstructures of particles.

Effect of Particle Shape on Cyclic Shear Behavior of Granular Mixtures–Geogrid Interface

The cyclic shear stiffness and damping ratio of angular and round particle geogrid interfaces is of much concern in reinforcement structure seismic analysis. In this study, various component percentages of crushed limestone and spherical granular medium mixtures were used to investigate the role of particle regularity in static and cyclic direct shear tests. The test results revealed that an increase in the proportion of round particles decreased cyclic shear strength and volume change. The phenomenon of shear softening was observed with a high amplitude of shear displacement when the proportion of round particles was increased in the mixture. As the percentage of round particles increased, the maximum interface shear stiffness decreased significantly from, 39.69 to 28.28 MPa/m, but a reverse trend in the maximum damping ratio was observed, from 0.308 to 0.37. The effect of cyclic shear history and proportion of round particles on interface strength parameters was also analyzed. A linear regression model was fitted to the data for quantifying the relationship between the proportion of round particles and friction angle. The results suggest that different percentages of round and angular particles can produce varying degrees of particle interlock between aggregate and geogrid, influencing the macro-mechanical behavior of the reinforced soil interface.

Bruggeman homogenization of a particulate composite material comprising truncated spheres and spheroids

Closed-form expressions were established for depolarization dyadics for a truncated sphere and a truncated spheroid, both electrically small, immersed in a uniaxial dielectric ambient medium. These depolarization dyadics were used to develop the Bruggeman homogenization formalism to predict the relative permittivity dyadic of a homogenized composite material (HCM) arising from a randomly distributed mixture of oriented particles shaped as truncated spheres and spheroids. Unlike other homogenization formalisms, most notably the Maxwell Garnett formalism, the Bruggeman formalism is not restricted to composites containing dilute volume fractions of constituent particles. Numerical investigations highlighted the anisotropy of the HCM and its relation to the shapes of the constituent particles and their volume fractions. Specifically, greater degrees of HCM anisotropy arise from constituent particles whose shapes deviate more from spherical, especially for mid-range volume fractions.

Compaction behavior of coarse-grained soil under various vibration frequencies: a DEM study

PurposeThis paper investigates the vibration compaction mechanism and evaluates the impact of vibration frequencies on the stability of coarse-grained soil, aiming to optimize the subgrade filling process.Design/methodology/approachThis study examines the vibratory compaction behavior of coarse-grained soils through indoor vibration tests and discrete element simulations. Focusing on angular gravel (breccias) of varying sizes, the simulations were calibrated using parameters such as Young’s modulus, restitution and friction coefficients. The analysis highlights how particle shape influences compaction, revealing mesoscopic mechanisms that drive macroscopic compaction outcomes.FindingsThis study investigates the influence of vibration frequency on the compaction behavior of coarse-grained soils using discrete element simulation. By analyzing particle contact and motion, the mesoscopic mechanisms driving compaction are explored. The study establishes a positive linear correlation between contact force anisotropy (Cv) and deformation, demonstrating that higher anisotropy leads to greater structural disruption. Additionally, the increase in sliding contact percentage (SCP) at higher frequencies indicates instability in the skeletal structure, driven by uneven contact force distribution. These findings reveal how frequency-induced stress concentration affects the stability and deformation of the soil skeleton.Originality/valueThis research explores the effect of various vibration frequencies on the compaction behavior of coarse-grained soils, examining microscopic interactions to reveal their impact on soil stability and deformation.

Modelling of precipitate hardening in ferroelectric materials

AbstractThis investigation presents a mechanical model to determine energetically favourable particle shapes, motivated by precipitation hardening in ferroelectric materials. We examine Li-doped $$\text {NaNbO}_3$$ NaNbO 3 and propose a system of equations to derive the correct material constants for this material system. To model the elongated precipitate shape we introduce two approaches: An elliptic shape and a shape based on cubic B-spline-curves. We subject both definitions to an optimisation routine that yields equilibrium shapes. We further use the spline approach to derive configurational forces on the interface.

Methods to identify and distinguish the effects of weathering and landslides on sediment granulometry

Urbanization has resulted in the widespread development of built-up areas, often without considering the local geology and geomorphology. To improve risk assessments related to landslides, it is essential to determine the physical and chemical properties of sediments. The aim of this study is to exemplify an already mobilized and reworked layer based on granulometric properties of the sediments and characterize the chemical and physical properties which have changed during or after the mass movement. Ten red clay layers were sampled near Kulcs (Hungary) from a sliding surface and its environment. We measured grain size distribution, major element and modal composition, furthermore, conduct particle shape analysis, respectively. Grain size distribution suggest that samples from the sliding surface are weathered, with the exhibiting reworking characteristics. We calculate the weathering index from the major elements, which, in combination with the particle shape analyses of the silt fractions, indicate that the morphological parameters of the samples are in relation with weathering index. According to our results, while a fresh sliding event leaves marks on the granulometric properties, the main process which affects the grain morphology is the chemical abrasion (post the mass movement) and not the landslide event.

The Influence of Fibers from Domestic Laundry Wastewater on the Clogging Process of a Filter

This study presents the impact of the size and shape of particles in laundry wastewater on the clogging process of a porous material. Clogging can be defined as a mechanical limitation of flow through porous media. The process of mechanical clogging was investigated in this study. The research was conducted in laboratory conditions in a filter column filled with glass beads whose diameter corresponded to coarse sand. The results reveal the influence of graywater quality on filter hydraulic conductivity and bed clogging, showing the impact of fiber particles in wastewater (sewage from home laundry) on the clogging process in soil. The results confirm that fiber particles significantly reduce filter permeability, particularly due to the formation of a filter cake. As analyzed in this paper, the distribution of quantitative data on particles of different sizes found in laundry wastewater indicates that they mainly accumulate in the upper layer, where particles with fiber lengths ranging from 0 to 1600 µm can be found. The average length of the fibers decreased with increasing depth. At a depth of approximately 10 cm, fibers with dimensions in the range of 0 to 100 μm were predominantly observed.

Homogenization of a random mixture of identically oriented superspheroidal particles

Depolarization dyadics were computed for superspheroidal particles made of an isotropic dielectric material and immersed in a uniaxial dielectric material. Superspheroidal shapes of two kinds were considered: one intermediate between spheroidal and cylindrical, and the other intermediate between spheroidal and cuboidal. These depolarization dyadics were employed in the Maxwell Garnett and Bruggeman homogenization formalisms to estimate the relative permittivity dyadics of homogenized composite materials (HCMs) that are random mixtures of identically oriented superspheroidal particles. The anisotropy of the HCMs was exposed through numerical investigations which revealed the dependencies of the HCM's anisotropy upon the shapes of the constituent particles and their volume fractions. The largest degrees of HCM anisotropy arose when the shape of the constituent particles deviated most from spherical, especially at mid-range volume fractions. Estimates of HCM anisotropy from the Maxwell Garnett and Bruggeman formalisms were broadly similar over the volume-fraction range appropriate for the Maxwell Garnett formalism, with modest differences being most apparent for particle shapes that deviated most from spherical.

Sanding Performance and Wear Mechanism of Precision-Shaped Abrasive Belts for Medium-Density Fiberboard

Sanding in medium-density fiberboard (MDF) often encounters unstable quality and premature failure, primarily because there is currently no abrasive belt specifically suitable for MDF sanding characteristics. We designed two precision-shaped abrasive belts (PSAs) for MDF and herein report on the characteristics. The material removal process for PSA was divided into three phases; the most stable, phase II, represents the effective working period. Compared to the contrast accumulated abrasive belt, PSAs achieve 16.12 and 11.10 times higher surface quality based on the mean value of roughness parameter Sa, achieving 1.34- and 2.0-, and 15.61- and 8.54-times-higher stability in material removal and surface quality based on the mean deviation. Wear patterns on PSAs include large abrasive wear, micro-abrasive fall-off, fracture, and wear, avoiding premature failure due to blockage and promoting long-term and efficient sanding. The uniform shape, height, and distribution of particles in PSAs results in excellent sanding performance. This study provides the foundation for further research on sanding mechanisms and PSA design for MDF.

On progressive failure of sand considering fabric evolution with micropolar hypoplastic model

To study the progressive failure of sand considering the multi-scale and its fabric evolution, the fabric is used as the quantitative link from micro to macro, then the influence of fabric on the anisotropic critical state is adopted to establish a hypoplastic model, and the fabric evolution and micropolar theory are employed to describe the mesoscopic mechanism of local deformation, finally, the simulations of discrete element methods (DEM) and finite element methods (FEM) is coordinated to reproduce the progressive failure. In the DEM biaxial simulations, the distribution of the contact normal is quantitatively determined by the novel orthotropic fabric tensor, and the difference in particle shapes and sample position showed that the fabric evolution is obvious, especially inside and outside the shear band, and before or after the shear band penetration. The fabric evolution of DEM is implanted into the corresponding location of the FEM sample, the results indicate that the macro-meso incorporation hypoplastic model can effectively describe strain localization evolution and progressive failure. The internal length of micropolar theory and particle size are identified as the main factors influencing the shear band thickness. The anisotropic fabric influences the shear band patterns, with circular and elliptical particles tending to form an "X-shape" shear band, while square and triangular particles tend to form a "L-shape" shear band.

Multiscale evaluation of sand-geomaterial interface shear response in terms of material geometry effects

This study evaluates the effects of particle and surface geometric features on the interface shear behavior of sand-geomaterial. Particle shape and size were adjusted for the sand, and surface roughness form and height were set for the geomaterial part. 3D printing technology was used to produce geomaterials in the desired form. A custom-made transparent interface shear box was developed to perform digital image processing. For macroscale response, peak and residual strengths and dilation angle were measured. Sliding percentage and shear band thickness were determined from digital image correlation analyses for the mesoscale response. The experimental results showed that the macroscale response parameters increased as the overall regularity of the sand particles decreased. The increase in mean particle size and roughness height led to an increase in macroscale parameters. Digital image correlation analyses showed that the sliding percentage had an inverse correlation with the shear band thickness in terms of the particle shape and the roughness height effects. The roughness form controlled the trend of mean particle size effects on the sliding percentage. Overall, the mesoscale parameters revealed the traces of interlocking response, particle kinematics, and the failure mechanism in the interface region. Thus, a bridge was established between meso- and macro-scale responses.

Fragmentation characteristics of abrasive particles for hard rock drilling with waterjet energy parameter

The use of abrasive waterjets (AWJs) for rock drilling offers advantages in urbanized areas, locations that are vulnerable to damage, and piling operations. However, the overall operational cost of AWJ systems remains high compared to that of conventional drilling methods, which constrains the long-term industrial application of AWJs. For instance, the abrasive costs account for over 60% of the total process cost, but the recycling of abrasives remaining after drilling could significantly reduce machining costs. In this study, the post-impact characteristics of abrasives were explored, aiming to enhance their recyclability. The physical properties and particle distribution of used abrasives vary depending on the jet energy, ultimately affecting their recyclability and recycling rate. The particle properties of used abrasives (particle size distribution, particle shape, and mean particle size) were compared under different waterjet energy variables (standoff distance (SOD) and water pressure) and test conditions (dry and underwater). Furthermore, the collision stages of the abrasive particles within a waterjet system were classified and analyzed. The results revealed that abrasive fragmentation predominantly occurred due to internal collisions within the mixing chamber. In addition, an attempt was made to optimize the waterjet parameters for an economical and efficient operation. The findings of this study could contribute to enhancing the cost-effectiveness of AWJ systems for rock drilling applications.

Vertical Variability in morphology, chemistry and optical properties of the transported Saharan air layer measured from Cape Verde and the Caribbean.

The structural properties of the Saharan air layer (SAL) including chemical, morphological and optical properties were measured during the Saharan Aerosol Longrange TRansport and Aerosol Cloud interaction Experiment (SALTRACE- June/July 2013). Flight measurements were done from Cape Verde and the Caribbean. Changes happening with the chemical composition, mixing, shape and absorption of aerosol single particles (particle diameter range 0.5-3.0 µm) inside SAL during its transport are detailed. Dust-dominated SAL (relative number abundance >90%) and generally low mixing (<1% with sea-salt and sulphates) are observed at both locations. The change in shape (determined as aspect ratio (AR)) after transatlantic transport was statistically not significant. The iron oxide fraction, important for light absorption, contributed 6.0-6.8% to SAL dust. A lower amount of Fe oxides was observed in transported SAL, especially for the size range 0.5-1.5 µm. This reduction in Fe oxide content resulted in a 4% decrease (0.0046-0.0044) in dust imaginary refractive index and a 1% decrease in single scattering albedo (0.802-0.809) at 520 nm. Our work suggests including the size distribution of iron oxides and their particular behaviour in future experiment/model studies.

Coupled Effects of Particle Shape and Grain-Scale Deformability on Repose Angle of Sand–Rubber Granule Mixture

Coupled Effects of Particle Shape and Grain-Scale Deformability on Repose Angle of Sand–Rubber Granule Mixture

Eulerian multi-fluid simulations of local liquid distribution in a bed packed with cylindrical particles

Packed bed reactors (PBRs) are extensively used in chemical process industries to perform solid-catalyzed gas–liquid reactions. Their performance is significantly influenced by liquid distribution which is a strong function of particle shape and size. In the present work, we simulated the steady-state local liquid distribution, pressure drop (ΔP/L), and overall liquid holdup (〈εL〉) for the beds packed with spherical and cylindrical particles using a three-dimensional (3D) Eulerian multifluid model and validated the predictions using corresponding high-speed imaging measurements performed in pseudo-2D packed beds. We showed that the Eulerian model with existing closures significantly underpredicts the liquid distribution for the bed randomly packed with cylindrical particles. To address this, we proposed a modification in existing mechanical dispersion force (F→D) model as a function of average particle orientation angle (θ). The modification significantly improved agreement between the predictions and the corresponding measurements. Using the modified model, we showed that the increased magnitude of F→D in the lateral direction leads to higher lateral liquid spreading for cylindrical particles as compared to that for the spherical particles. Importantly, the modified model also predicted the local liquid distribution and ΔP/L for beds packed manually with cylindrical particles oriented at different θ in a satisfactory agreement with the corresponding measurements. On increasing θ, the F→D in lateral direction (i.e., perpendicular to flow) as well as liquid–solid interaction force (F→LS) in axial direction (i.e., parallel to flow) found to increase significantly. As a result, the lateral liquid spreading as well as ΔP/L decrease substantially on increasing θ.

Impact of grinding media shape on the dissociation characteristics and flotation behavior of coking coal middlings

The effective dissociation of feed materials has a major impact on the mineral flotation recovery performance in the mineral processing field. Coking coal middlings is difficult to be effectively dissociated due to its complex internal gangue distribution characteristics. The aim of this paper is to compare and evaluate the performance of ball versus hexagonal prism media for the coking coal middlings comminution by point contact and line-surface contact. The results of the grinding tests show that hexagonal prism could result in a more uniform coal particle size distribution, less over-grinding and better selective dissociation effect comparing with ball. The results of the particle shape coefficient indicate the hexagonal prism milled product has a sphericity (Rs) of 0.90 and an elongation (EW) of 1.69, which is more slender than the ball milled product (Rs = 0.94, EW = 1.47). Flotation tests showed that the hexagonal prism milled product was more hydrophobic with a wrap angle of 185° compared to the ball milled product at 121°. Meanwhile, the TSI value of the hexagonal prism milled product is 80.500, which is lower than the 82.608 TSI value of the ball milled product, indicating that the flotation system of the hexagonal prism mill product is more stable. Under the same flotation test conditions, the combustible matter recovery rate of the hexagonal prism milled product was 5.08 % higher than that of the ball milled product.

Study on micromechanical behavior and energy evolution of granular material generated by latent diffusion model under rotation of principal stresses

In this study, advanced image processing technology is used to analyze the three-dimensional sand composite image, and the topography features of sand particles are successfully extracted and saved as high-quality image files. These image files were then trained using the latent diffusion model (LDM) to generate a large number of sand particles with real morphology, which were then applied to numerical studies. The effects of particle morphology on the macroscopic mechanical behavior and microscopic energy evolution of sand under complex stress paths were studied in detail, combined with the circular and elliptical particles widely used in current tests. The results show that with the increase of the irregularity of the sample shape, the cycle period and radius of the closed circle formed by the partial strain curve gradually decrease, and the center of the circle gradually shifts. In addition, the volume strain and liquefaction strength of sand samples increase with the increase of particle shape irregularity. It is particularly noteworthy that obvious vortex structures exist in the positions near the center where deformation is severe in the samples of circular and elliptical particles. However, such structures are difficult to be directly observed in sample with irregular particles. This phenomenon reveals the influence of particle morphology on the complexity of the mechanical behavior of sand, providing us with new insights into the understanding of the response mechanism of sand soil under complex stress conditions.

Role of particle shape in sheared granular media: Roundness and elongation

Role of particle shape in sheared granular media: Roundness and elongation

GPU based discrete element modeling for convex polyhedral shape particles: Development and validation

Particle dynamics simulations face a significant challenge in understanding the intricate behaviors of convex polyhedral particles due to their complex geometries and interactions. DEM emerges as a key method, illuminating the concealed intricacies of these geometric entities. Traditional algorithms often require cumbersome processes to check each type of contact individually. However, Gilbert-Johnson-Keerthi’s (GJK) and the expanding polytope algorithm (EPA) provide efficient numerical solutions for polyhedral contact detection and contact resolution. These Minkowski difference-based methods streamline contact detection and overlap computation, paving the way for deeper exploration of three-dimensional contact theory within DEM simulations. By leveraging GPU computational power, this paper outlines key algorithmic steps and verifies the code’s accuracy through comparison with simulated and experimental data, with an average deviation of less than 5%. This study explores the impact of particle shape on the dynamics and mechanical behavior of densely packed systems, particularly in hoppers and tumblers. Spherical particles discharge faster but mix more slowly than polyhedral shapes, with icosahedrons achieving quicker full mixing. These results align with experimental findings, further validating the simulation approach.

Investigations on the rheological properties of cement mortar based on fine aggregate characteristic and its extended prediction model

The rheological property of mortar is significantly influenced by its contained fine aggregate morphology characteristic and capable predictive models are limited. This work aims to expand the film thickness theory by developing an index that integrally represents variations in grain shape, gradation, and mix proportions, and elucidates the impact and the mechanism of these multifactorial differences on rheological performance. The quantitative analysis of the aggregate gradation and particle shape differences were performed, which was used to assess the impact of these variations and different mix ratios on the rheological performance of mortars. A correlation between aggregate differences and film thickness was established using specific surface area and void ratio. The result shows that variations in aggregates are accurately assessed by image analysis and consistently reflected in specific surface area and void ratio metrics. Since variations in rheological performance are predominantly governed by differences in film thickness, the disparities among aggregates can be quantified in terms of their impact on rheological properties by considering specific surface area and void ratio, thus translating into variations of film thickness. The differences in rheological properties due to variations in grain shape, gradation, and mix proportions can be comprehensively represented and controlled through an expansion of the film thickness model.