Granular Matter最新文献

Firework oxidizer powders are inorganic compounds that supply active oxygen within pyrotechnic systems. Due to their fine particle size and tendency to leak during handling, accurately simulating their flow behavior is essential for optimizing powder-filling equipment. However, limited research exists on their discrete element method (DEM) parameters, and many key contact properties remain undocumented. This study systematically calibrated six critical DEM contact parameters for firework oxidizer powders-particle density, elastic modulus, Poisson’s ratio, static friction coefficient, rolling friction coefficient, and shear modulus-using a combination of experimental measurements and numerical simulations. The Hertz-Mindlin contact model was adopted, and a Plackett–Burman design was used to identify the most influential parameters affecting the static angle of repose. Results showed that the static friction coefficient, rolling friction coefficient, and shear modulus had the most significant effects. Their optimal ranges were further refined via steepest ascent testing. A Box-Behnken design was employed to develop a regression model for the angle of repose, yielding final calibrated values of 0.288, 0.035, and 65.076 MPa for the three dominant parameters, respectively. These parameters were then applied in DEM simulations of powder flow involving a T-shaped scraper, which pushes the powder toward the dosing holes, allowing it to fall under gravity. Physical filling tests demonstrated that powder leakage was effectively controlled when the scraper speed did not exceed 0.3 m/s. This study provides valuable insights for equipment optimization and offers a reliable reference for DEM-based modeling and design of firework oxidizer powder handling systems.

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Baffles is an effective means of preventing and controlling rock avalanches, but the blocking performance of particle splashing in rock avalanches is not yet clear. And the particle shape has a significant impact on the dynamic characteristics of particle splashing. This study reviewed the research and application of baffles in avalanches, debris flows, and rock avalanches and adopted Discrete Element Method (DEM) software to conduct numerical simulation experiments, comparing the motion characteristics and energy evolution of particle splashing in rock avalanches with various shape particles under baffles protection, analyzing the motion mode of particle splashing, and assuming the internal mechanism of shape affecting particle splashing. The results showed the splashing particle mass, peak particle velocity, maximum splashing distance, and average splashing height of particles with different shapes are roughly linearly and negatively correlated with the particle shape factor with the maximum difference of 2166.0, 25.2, 98.5 and 10.2% respectively, while the relative energy consumption of particles during the sliding motion is roughly linearly positively correlated. There are two modes of particle splashing, inter-particle collision and deposit body collision, changing the motion direction and velocity of splashing particles. The differences among the splashing motion characteristics of particles with different shapes result from the distinct collision modes induced by the collision angle, velocity, and spin, which can influence the direction and velocity of particles after collision. Based on our previous studies in baffle-net structures, the optimal engineering height of protective net was confirmed as 0.94 times of baffle height for the interception of particle splashing in rock avalanches reducing 86.5% splashing particles than the baffles with the protective net of 0.5 times baffle height, as reference for particle splashing prevention.

This study focuses on the dynamics of granular flow similar to landslides and avalanches using a controlled environment. The work experimentally investigates the gravity-driven granular flow to mitigate the threat of landslides using both dry and wet surfaces. For dry conditions, different friction surfaces are used, while for wet conditions, different water levels are employed. Granular flow is studied for different angles of inclination and compared using spread area, run-off distance, and height of the terminated flow. At lower angles, the run-off distance experiences a reduction of approximately 50% for the frictional surface. The study reveals the formation of distinct deposit patterns on the ground table, ranging from a mustache-like structure to a tongue-shaped structure for low to high friction conditions respectively. Additionally, it’s observed that a wider spread area is formed under both low and high friction conditions, but a narrow spread is observed for the medium friction surface. For medium friction, there exists a balance between energy dissipation due to particle –surface collisions and particle momentum loss affecting the spread formation. The granular flow entering the water is divided into a leading wave at the top surface and a turbidity current, which is propagated along the bottom surface of the water. The medium friction surface presents a viable strategy for enhancing resilience against landslide. Additionally, the potential use of water bodies as a control measure shows promising results. These findings contribute to a deeper understanding of granular flow behavior and the development of effective control measures in landslide-prone regions.

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Deposition pattern and spread area comparison

This article explores the hysteretic behavior and the damping features of sheared granular media using discrete element method (DEM) simulations. We consider polydisperse non-cohesive frictional spherical particles, enclosed in a container with rigid but moving walls, subjected to a cyclic simple shear superimposed on a confining pressure. The mechanical response of the grains is analyzed in the permanent regime, by fitting the macroscopic stress–strain relation applied to the box with a Dahl-like elasto-frictional model. The influence of several parameters such as the amplitude of the strain, the confining pressure, the elasticity, the friction coefficient, the size and the number of particles are explored. We find that the fitted parameters of our macroscopic Ansatz rely qualitatively on both a well-established effective medium theory of confined granular media and a well-documented rheology of granular flow. Quantitatively, we demonstrate that the single degree-of-freedom elasto-frictional reduced model reliably describes the nonlinear response of the granular layer over a wide range of operating conditions. In particular, we show that the mechanical response of a granular slab under simple shear depends on a unique dimensionless parameter akin to an effective Coulomb threshold at low shear/high pressure. Furthermore, exploring higher shear/lower pressure, we evidence optimal damping at the crossover between a loose unjammed regime and a dense elastic regime.

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Optimizing vibrations mitigation by confined elasto-frictional particles with a DEM-based Dahl-like reduced model

The principle of detailed balance (DB) states that every kinetic transition in a system with many micro-states, (mu ), is balanced, on average, with the opposite transition, (mu _ileftrightharpoons mu _j). The current perception is that, on the scale of the most elementary degrees of freedom, DB is satisfied only in equilibrium systems, although a rigorous proof exists only for thermal systems. It is believed that, on this scale, non-equilibrium steady states can only be balanced by cycles, such as (Arightarrow Brightarrow Crightarrow A). We report here experiments on a family of out-of-equilibrium quasi-statically cyclically sheared granular systems, which appear to show robust DB. We then analyse in detail the concept and interpretation of DB and show that our systems are the exact equivalent of chemically reactive systems in thermal equilibrium. We therefore conclude that our non-equilibrium systems do indeed satisfy this principle. We further study the approach to DB as a function of system size and time. Given the significant progress to which this principle has led in equilibrium systems, these observations may pave the way for better models of the dynamics and statistical mechanics of these and potentially other non-equilibrium systems.

Laser powder bed fusion (LPBF) is an additive manufacturing technique that utilizes laser-induced melting of specific regions within a powder layer to create complex parts. Achieving high-quality products in LPBF requires the optimization of process parameters based on the unique characteristics of the powder material. Since experimental optimisation can be both time-consuming and costly, we propose a computational model capable of simulating the particle micro-mechanics in LPBF, offering a more cost-effective solution.

We have developed a novel thermal discrete particle and contact model that accurately captures the essential phenomena of melting, coalescence, and consolidation within LPBF. Our model assumes that solid particles partially melt under the influence of heat, subsequently coalesce, and form solid bonds during the cooling phase. The rate of coalescence is determined by the material’s surface tension and viscosity as it undergoes melting. To account for phase transitions, we employ an apparent heat capacity method. We first introduce our contact model and provide verification against analytical solutions for a two-particle system. We then demonstrate the efficacy of our model by applying it to a multi-particle example, successfully capturing the coalescence and consolidation behaviour observed in LPBF. The model has been implemented in the open-source code MercuryDPM. The current model is developed for polymer material, but it can be extended to metal and ceramic.

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Thermal Discrete Particle Model of Particle melting and Coalescence

Driven by the “dual carbon” strategy for low-carbon steel transformation, raising the pellet ratio in the blast furnace (BF) burden offers a core technical path to optimize burden structure and cut carbon emissions. The distribution of BF burden critically influences operation by affecting internal gas flow, heat and mass transfer, and chemical reactions. This study employs the discrete element method (DEM) to examine how burden structure affects bed porosity at high pellet ratios, emphasizing mixed-layer formation. Key findings include: (1) Porosity evolution patterns in mixed burden layers under varying furnace charge configurations were characterized. (2) Porosity is minimized at the ore-coke interface because of particle penetration. Additionally, this effect intensifies as the coke-ore size difference increases. (3) Increasing the pellet ratio enhances lump-zone bed porosity and permeability. As the pellet ratio increased from 30 to 90%, bed porosity rose from 33.75 to 36.19%, a 2.43% increase.

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In this study, a contact-scale approach is developed in order to measure the strength of the bio-cemented bond under shear loading. Fifteen pairs of bio-cemented sand grains, coming from two different bulk samples with different calcite content, were first observed using high-resolution synchrotron X-ray tomography in order to compute the contact surface area, before being subjected to the shear loading. After failure, these samples were also observed using scanning electron microscopy and energy-dispersive X-ray spectroscopy in order to determine the failure mode. The results have shown that the shear strength is 2.11 times higher that the tensile strength for this material, and has an average value of 5.81 ± 1.99 MPa. Digital image correlation was used in this study in order to distinguish the samples that broke due to shear from those that broke due to rolling. Similarly to the case under tensile loading, failure was also observed to occur at the interface between the sand and the calcite crystals. The percentage of active calcite crystals (hbox {f}_textrm{c}) was also found to be around 25%, independently of the amount of calcite present in the initial bulk sample.

Graphical Abstract

Main steps followed in the study that allow to find the shear strength of a bond between bio-cemented sand grains.

This paper investigates the effects of recent stress history (RSH), specifically sudden changes in the stress path direction, on the small-strain stiffness and stiffness degradation characteristics of granular materials, using three-dimensional discrete element method (DEM) simulations. Specimens with varying RSHs are prepared via a series of approach paths from diverse directions, involving deviations from and returns to a common stress state. The norm of the induced plastic strain, obtained through a stress probing technique, is proposed as a criterion to determine the extent of the approach path. Subsequently, constant-p triaxial compression tests are conducted to analyze the effects of different RSHs on stress–strain response, small-strain stiffness, and stiffness degradation. Results reveal that specimens experiencing full stress reversal exhibit significantly higher small-strain shear stiffness than those under sustained load directions. Specimens loaded with counterclockwise stress rotation angles exhibited slightly greater stiffness than those with equivalent clockwise angles. Furthermore, the configuration of stiffness degradation curves, defined by onset and reference shear strain, is strongly influenced by the stress rotation angle. Stress probing reveals that RSH mainly affects total shear stiffness degradation by altering the extent of plasticity, with the elastic stiffness remaining largely unaffected. Finally, a modification to an existing stiffness model is proposed by introducing an RSH-dependent factor, complementing the effects of void ratio, stress state, and shear strain, to enhance predictive accuracy.