Granular Matter最新文献

Screening Efficiency (SE) and Screen Surface Load (SSL) are important factors for the vibrating screening process design. In this work, inherent mechanism for the collaborative optimization of SE and SSL in our previous study is further explored numerically. Firstly, the particle-screen collision motion and the particle swarm screening motion are studied to reveal the SE&SSL related particle behavior. Then, the particle swarm behavior characteristics in both high SSL and low SSL modes are comparatively studied. In addition to enhanced local screened particles mass uniformity, the low SSL mode is about 47% lower in particle mass and 55% faster in flow velocity. Finally, the correlation between particle swarm behavior and process parameters, leading to high SE and low SSL, has been summarized. With small vibration amplitude 4.3 mm, low frequency 13 Hz and small vibration direction 50°, the vibration intensity (:{K}_{v}) is maintained at the lowest level 2.24, which indicates small particle-screen impact force and short throwing cycle. A large inclination angle 4.7° helps release the gravitational potential energy of particles, together with the small vibration direction, resulting in a rapid flow velocity, which suggests low particles mass. While small impact force and low particles mass are beneficial to the SSL reduction, rapid flow velocity with short throwing cycle, enabling sufficient particle-screen contacts, tends to maintain the high SE. This paper provides a deeper insight into the mechanism of high-performance vibrating screening.

Graphical abstract

Soil penetration, a typical process of driving a penetrator into soil at a constant speed, is common in geotechnical engineering. In addition to this pure penetration movement, natural organisms also employ rotational motions in their burrowing strategies, which are believed to reduce penetration resistance and are beneficial for the design of self-burrowing robots. In this study, the three-dimensional discrete element method (DEM) was employed to investigate the effect of confining pressure on the reduction of rotation-induced penetration resistance. It is observed that the rotation-induced reduction in penetration resistance weakens progressively with increasing confining pressure. This study investigates the underlying mechanisms of rotational and confining pressure effects from a microscopic perspective by combining complex network analysis. The introduction of rotation not only markedly reduces the number of particles in contact with the penetrator but also reorients particle displacement toward the horizontal direction, providing greater space for the penetrator to advance. However, increasing confining pressure suppresses dilatancy, resulting in larger vertical components of particle displacement and a greater alignment of tangential contact forces beneath the cone along the vertical direction. The denser and more stable particle structure manifests in higher average degree and clustering coefficient. Moreover, a distinct linear relationship is identified between the weighted average degree and the stable value of penetration resistance, bridging microscopic network features with macroscopic response.

We examined the influence of siliciclastic coating on the tribological behavior of sand particles. A new coating method was developed for this purpose, which is based on the principle of precipitation, allowing for a fairly uniform distribution of the microparticles to be developed, achieving a higher consistency of the test results in the normal and tangential directions to particle contacts. The investigation included both monotonic and cyclic tests as well as the application of preloading in some of the experiments. Particular emphasis was placed in the data analysis including contact Young’s modulus, coefficient of friction, contact stiffness in the normal (K_N) and tangential (K_T) directions and the stiffness ratio (K_N/K_T), as well as the analysis of elastic and plastic fractions of displacement, work done and the energy dissipation at the contacts of the particles. While the siliciclastic coating had a major influence on the contact stiffness and friction, the mechanisms of friction would be rather controlled by both the interlocking and inference of the microparticles as well as asperity interlocking of the sand grains, as revealed from post-shearing image observations. Overall, the contact behavior and the role of microparticle coating may be considered a key in understanding the meso- and macroscopic mechanics of granular systems and the mechanisms of energy dissipation.

Graphical Abstract

Static fatigue refers to the failure of materials under sustained stress levels lower than their short-term strength, which significantly affects the long-term stability of structures built on or within calcareous sand. This study investigates the progressive static fatigue behavior of calcareous sand, a material widely encountered in geotechnical engineering. Despite its widespread distribution, the underlying mechanisms governing the time-dependent mechanical degradation of calcareous sand remain insufficiently explored, necessitating further research. In this work, we employed an advanced non-destructive monitoring method, acoustic emission (AE) technology, to track real-time internal microstructural evolution, enabling a more detailed investigation of progressive failure mechanisms at a microscopic scale. Specifically, AE parameters such as hit rate and frequency characteristics are analyzed to provide quantitative insights into the initiation and propagation of micro-cracks. By utilizing AE monitoring, this research systematically evaluates the time-dependent mechanical degradation of calcareous sand under sustained loading, identifying key AE signatures associated with different phases of the static fatigue process. The findings offer valuable insights into the micro-mechanical behavior of calcareous sand during sustained loading, contributing to a better understanding of its long-term deformation and failure characteristics in engineering applications.

In the field of geotechnical engineering, the evaluation of passive earth pressure on retaining walls is crucial. Due to the heterogeneity of soil, soluble minerals tend to aggregate. The localized dissolution of soluble minerals reduces soil strength, which in turn may cause an overestimation of the passive earth pressure on retaining walls. In this study, the Discrete Element Method (DEM) was employed to illustrate the impacts of localized dissolution on passive earth pressure through pressure dissolution. The influences of the size and location of dissolvable zones on passive earth pressure under translation mode were analyzed. The results demonstrated that an increase in the size of the dissolvable zones correlates with a gradual decrease in the passive earth pressure. When the wall displacement is minimal, the passive earth pressure decreases as the dissolvable zone approaches closer to the moving retaining wall and the bottom of the backfill. However, with greater wall displacement, the effect of the dissolvable zone’s location on passive earth pressure becomes less pronounced. The presence of dissolvable zones in critical areas, coinciding with the plane of shear failure surface in the absence of dissolution, leads to a significant reduction in the shear strength of the backfill. Furthermore, variations in the size and location of the localized dissolvable zone impact the distribution of force chain and formation of shear bands.

Graphical Abstract

Understanding the stick-slip instability of granular materials is crucial to studying the quasi-periodicity of fault slip. The macroscopic frictional responses have inferred that particle size is one of the notable variables. To reveal the micro-mechanical cause, we analyzed the frequencies of Acoustic Emission (AE) events induced by the glass bead deformation through the compression tests and examined the effects of particle diameter on the stick-slip mechanism. We found that AEs distribute in the three frequency bands during the direct shearing process, with the probability density reflecting the three-stage evolution of force chains. At the microscopic scale, particle friction within the force chains induces micro-failures, generating low-frequency (0–100 kHz) AEs, as evidenced by environmental scanning electron microscopy. Meanwhile, high-frequency (200–350 kHz) AEs concentrate at the yield points. The probability density of AE events was used to quantify force chain deformation. The results show a negative correlation between AE rate and amplitude, with the micro-mechanical cause attributed to fewer frictional failures and an increase in critical elastic stiffness. The established AE-based experimental framework can provide insights into the micro-mechanisms of stick-slip instability.

Graphical Abstract

As a key operation in the bulk processing, particle mixing plays a crucial role in multiple industrial fields. In this study, the discrete element method (DEM) is used to investigate the mixing characteristics of non-spherical particles in a horizontal high shear mixer. Through quantitative analysis of Lacey mixing index, the effects of key parameters such as aspect ratio, particle shape, and rotational speed on mixing performance are discussed. The results show that the radial mixing efficiency of particles is significantly better than the axial mixing efficiency, and both increase with the increase of rotational speed. In addition, the mixing efficiency has a significant correlation with the flow resistance and energy transfer efficiency of particles. Specifically, in the axial direction, the hexahedral particles have the highest mixing efficiency, and the oblate spheroidal particles with AR = 0.25 have the lowest efficiency. In the radial direction, the hexahedral particles still maintain the highest efficiency, while the spherical particles with AR = 1 have the lowest efficiency.

Graphical Abstract

This paper carries out extensive simulations of granular columns composed of frictional-pentagonal grains, collapsing on a horizontal plane. Various two-dimensional columns are used and the interparticle friction coefficient is systematically varied in a broad range of values, aiming to comprehensively highlight and universally describe the runout distance, deposition height, area of top-deposition surface, kinetic energy, and apparent friction coefficient. We show that these physical quantities observed in this work are consistent with previous findings and are affected with the degrees depending differently on the initial column aspect ratio and interparticle friction coefficient. Remarkably, we nontrivially unveil a unified power-law scaling behavior for runout distance, deposition height, area of top-deposition surface, kinetic energy, and apparent friction coefficient by defining an effective aspect ratio, inversely incorporating the complex competition between initial aspect ratio and interparticle friction coefficient. This universal power-law description may confirm a unified competition of frictional and inertial effects on geophysical mass flows, providing a better understanding of the behavior of natural hazards such as rock avalanches and landslides.

Graphical Abstract

Collapse model and unified scaling behavior of thedeposition morphology and collapse mobility.

Understanding grain fragmentation in fault gouge is essential for capturing the mechanical behavior and evolution of fault zones under shear. In this study, we present a 2D Discrete Element Method (2D-DEM) framework that simulates comminution using angular, breakable grains, overcoming limitations of traditional models based on spherical particles. Our approach incorporates realistic fracture mechanics and grain geometries to better represent microstructural evolution during shearing. A series of numerical experiments, including Brazilian, oedometric, and shear tests, were conducted to calibrate the model and examine the roles of grain strength, friction, and Young’s modulus. The simulations reproduce key numerical observations such as strain localization, force chain evolution, and grain rounding through chipping mechanisms. Results show that the model captures the onset and progression of fragmentation, as well as its impact on fault strength and mechanical stability. A comparison with a dedicated laboratory experiment is provided. This work provides a robust numerical tool for studying fault gouge behavior and lays the foundation for future studies exploring the influence of initial grain size and material properties on fault mechanics.

Graphical Abstract

A robust numerical tool with fragmentation for studying fault gouge behavior

Three phase granular mixes consisting of soft (recycled tyre aggregates) and rigid (crushed rock) materials bonded with flexible or semi-flexible binders are gaining momentum as a solution for waste tyre crisis. Experimental works suggest macro-scale responses of these mixes are dependent on both soft and binder content in the mix. However, the underlying mechanisms governing these responses remain unclear. The present study focuses on exploring the contact mechanics of three-phase granular mix composed of soft and rigid particles bonded with flexible binders. Conventional contact laws for particle-scale study of bonded materials have limitations, as they are primarily formulated for rock-like materials. Therefore, advanced contact models are necessary to understand the macroscopic behaviour of these three-phase granular media. Given the flexible nature of the binder in this study, the ‘softbond model’ is employed to simulate the behaviour of the three-phase mix. However, the softbond model overestimates the strength of these granular mixes by assuming identical contact stiffness for bonded and unbonded conditions. The compressibility of unbonded contact is significantly different from the bonded contacts due to the presence of soft particles. To address this contact stiffness disparity, the softbond model is enhanced to better simulate the contact behaviour of these mixes. The new modified model can accurately predict the constrained modulus evolution against axial stress as found in one-dimensional compression experiments in the literature. Microstructural analysis of these mixes provides valuable insights into bond breakage, force distribution, and strong force chains. Bond breakage alters the force chain distribution in these mixes, and despite the presence of bonds with higher stiffness, unbonded contacts begin to dominate the force chain. The variation in microstructural properties indicates that the behaviour of these mixes depends not only on the binder content but also on the proportion of soft particles in the mix. The new microstructural understanding will ultimately help proposing better hypothesis to explain the complex material response for different soft and binder contents under applied loading.