Granular Matter最新文献

The mechanics of granular materials at the macroscopic scale inherently depends on the particle interactions occurring at the microscopic scale. In recent decades, growing investigations have explored the mechanics of granular materials subjected to thermal cycles, as they involve complex responses that bear significance for science, engineering, and technology. However, the fundamental understanding of the mechanics of granular materials subjected to thermal cycles remains hindered by the absence of empirical evidence into the microscopic particle interactions that govern the macroscopic response of such materials. For the first time, this study presents direct experimental evidence obtained via synchrotron X-ray microtomography to reveal the behavior of the particles that constitute granular materials during thermal cycling. This work experimentally confirms the existing theory by which thermally induced particle interactions drive a macroscopic volumetric expansion and contraction of granular materials upon heating and cooling, respectively, and the development of irreversible volumetric deformations upon the completion of thermal cycles. The results uncover the evolution of particle non-uniform translations, rotations, and contact variations during thermal cycling, which all inherently depend on particle shape.

This study investigates the influence of particle shape on the void space morphology and topology in granular materials. Numerical samples with spherical and ellipsoidal particle shapes were generated using the discrete element method. A segmentation algorithm was used to extract the pore space characteristics. The results reveal that particle shape significantly affects both constriction and pore sizes, with distinctive features according to flatness index or elongation ratio, the former being more significant than the latter. The obtained results were validated by conducting numerical filtration tests, which illustrated a direct correlation between the constriction properties derived from the pore space extraction and the blockage rate of fine particles in the filtration tests. The study revealed the importance of considering particle shape in filter design, emphasising its significant impact on pore space characteristics and filtration performance.

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This study presents a discrete element numerical model for the unidirectional compaction of microfine magnesite powder, designed to enhance the green body density based on laboratory apparatus configurations. The research demonstrated that as particle size decreased, porosity significantly reduced and density increased, resulting in a more uniform internal distribution within the green body. This led to closer particle contacts and an increased coordination number, which in turn intensified inter-particle interactions and the effectiveness of force transmission. During compaction, the distribution of force chains became more uniform, reducing localized stress concentrations and enhancing the mechanical integrity of the green body. The stress–strain relationship followed a polynomial pattern, highlighting the significant influence of particle size on the mechanical behavior during compaction. These findings provide a valuable theoretical basis for optimizing the compression molding process of microfine magnesite powder, facilitating the production of high-density, high-performance molded products.

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Accurate simulation of laboratory undrained and cyclic triaxial tests on granular materials using the Discrete Element Method (DEM) is a crucial concern. The evolution of shear bands and non-uniform stress distribution, affected by the membrane boundary condition, can significantly impact the mechanical behavior of samples. In this work, the flexible membrane is simulated by using the Finite Element Method coupled with DEM. In addition, we introduce a hydro-mechanical coupling scheme with a compressible fluid to reproduce the different undrained laboratory tests by using the membrane boundary. The evolution of pore pressure is computed incrementally based on the variation of volumetric strain inside the sample. The results of the membrane boundary condition are compared with more classical DEM simulations such as rigid wall and periodic boundaries. The comparison at different scales reveals many differences, such as the initial anisotropic value for a given preparation procedure, fabric evolution, volumetric strain and the formation of shear bands. Notably, the flexible boundary exhibits more benefits and better aligns with experimental data. As for the undrained condition, the results of the membrane condition are compared with experimental data of Toyoura sand and rigid wall boundary with constant volume. Finally, stress heterogeneity during undrained monotonic and cyclic conditions using the membrane boundary is highlighted.

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The deformation of expansive soil in seasonally frozen regions caused by freeze–thaw cycles has severely affected the long-term performance of engineering applications. The alteration of expansive soil microstructure has resulted in many geotechnical engineering failures, such as soil cracking and settlement. Consequently, the micropore contraction and expansion mechanisms of expansive soil have drawn extensive attention. Nuclear Magnetic Resonance (NMR) is widely used as a rapid, non-destructive detection technique for moisture monitoring and microstructure evolution characterization in porous media. In addition, Magnetic Resonance Imaging (MRI) can visualize the migration pattern of pore water under different numbers of freeze–thaw cycles. SEM is the most effective and direct method to reveal the structure of particle and micropore arrangement. This paper investigates the pore size evolution and pore structure distribution characteristics of saturated expansive soil via 6 freeze–thaw cycle tests using NMR and SEM techniques. The evolution law of saturated expansive soil under freeze–thaw cycles is obtained. The results show that pore water migrates from the center to the periphery under freeze–thaw cycles. The pore size decreases as the number of freeze–thaw cycles increases and small particles increase significantly. During the freeze–thaw cycle, the arrangement pattern changed from surface-surface contact to stacking.

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