Computational Particle Mechanics最新文献

Railway operation in desert areas faces unique challenges due to wind-blown sand penetration on the safety of the line. In-depth research on the impact of wind-blown sand penetration on the shear performance of the railway ballast is crucial for understanding potential problems in sandy railways and formulating effective maintenance strategies. This paper conducts a series of direct shear tests under various sand contents and load conditions using an independently developed automatic control loading direct shear test apparatus suitable for railway ballast. By accurately considering the interaction between sand and ballast particles, some direct shear numerical models of different sand-containing ballast boxes based on refined particle simulation are established based on the discrete element method (DEM) and particle scaling method, exploring the variation in shear strength, shear deformation, contact relationships, and rotational characteristics of railway sand-containing ballast from macroscopic and microscopic perspectives. The results show that with the increase in shear strain, the shear stress of the ballast with various sand contents increases first and then tends to stabilize, and the phenomenon of dilation occurs in all cases. When the normal load is constant, the shear strength and cohesion of the ballast show a trend of first decreasing and then increasing with the increase in sand content. The wind-blown sand penetration inhibits the rotational deformation during shearing, enhancing particle aggregation. With the increase in sand content, the contact coordination number, powerful force chain number, and total force chain number all increase continuously. However, the average contact force shows a trend of gradually decreasing and then increasing. This study provides theoretical support and experimental backing for the operation and maintenance of the ballast bed in sandy railways.

In this paper, an accurate meshless method for solving time-fractional wave equation (TFWE) based on KDF-SPH approximation is proposed. In this method, finite difference method is used to discretize the time-fractional derivative defined in the Caputo sense. The spatial discretization is achieved using KDF-SPH meshless method. At the same time, the kernel approximation and particle approximation expressions are given. In order to prove the effectiveness and order of numerical convergence of the proposed method, a number of 1D and 2D initial boundary value problems are numerically simulated in regular and irregular domains, and the meshless method is compared with the existing methods. Numerical results show the effectiveness and accuracy of the proposed method, and the second-order accuracy is achieved in space in the regular calculation area.

A better understanding of the relevance between mixing and heat transfer of granular material is necessary for the design of mixers in various industries. In this work, the effect of impeller speed and filling rate on the mixing and heat transfer of granular material in a ribbon reactor was studied based on DEM simulations. Quantitative criteria which are characterized by the critical mixing time and critical heating time were proposed based on the simulation results. It was found that the area near the vessel wall is heated first, and then the top surface area and the region near the impeller shaft are heated sequentially due to the recirculation effect. Increasing the impeller speed and decreasing the filling rate can improve the mixing and heat transfer performance. The effects of impeller speed and filling rate on mixing and heat transfer weaken as they increase. Results obtained in this work indicate that increasing the mixing performance can enhance the heat transfer of granular material in the ribbon reactor.

Several gradations of concrete with fractal dimension D = 2.0–2.9 (i.e., 2.0, 2.2, 2.4 2.6, 2.7, 2.8, 2.9) were designed based on particle size-mass distribution fractal model. The random polyhedral aggregate model was generated and then imported particle flow code, the discrete element method (DEM), to establish a multi-phase model considering mortar, aggregate, and interfacial transition zone (ITZ). On this basis, the relationship between fractal dimension D and macro-mechanical properties and microstructure of concrete was discussed, and the grading evaluation index was proposed based on fractal dimension D. The results show that the number of large-size aggregates decreases with increase in the fractal dimension, the compressive strength of concrete increases and reaches the maximum when the fractal dimension D = 2.7. Meanwhile, the fractal dimension affects the failure mode, as fractal dimension D increases, the total microcracks gradually increase, among which the ITZ microcracks increase mainly. Compared with the uncertainty of the non-uniformity coefficient and curvature coefficient, the fractal dimension can more accurately describe the aggregate grading characteristics. In addition, appropriate adjustments should be made to determine the range of fractal dimensions considering the differences between the aggregate filling.

This paper aims to analyse electrical conduction in partially sintered porous materials using an original resistor network model within discrete element framework. The model is based on sintering geometry, where two particles are connected via neck. Particle-to-particle conductance depends on neck size in sintered materials. Therefore, accurate evaluation of neck size is essential to determine conductance. The neck size was determined using volume preservation criterion. Additionally, grain boundary correction factor was introduced to compensate for any non-physical overlaps between particles, particularly at higher densification. Furthermore, grain boundary resistance was added to account for the porosity within necks. For numerical analysis, the DEM sample was generated using real particle size distribution, ensuring a heterogeneous and realistic microstructure characterized by a maximum-to-minimum particle diameter ratio of 15. The DEM sample was subjected to hot press simulation to obtain geometries with different porosity levels. These representative geometries were used to simulate current flow and determine effective electrical conductivity as a function of porosity. The discrete element model (DEM) was validated using experimentally measured electrical conductivities of porous NiAl samples manufactured using spark plasma sintering (SPS). The numerical results were in close agreement with the experimental results, hence proving the accuracy of the model. The model can be used for microscopic analysis and can also be coupled with sintering models to evaluate effective properties during the sintering process.

Particle erosion is a major failure mechanism in thermal barrier coatings. In this work, a discrete element model is developed to simulate the crack propagation due to particle erosion. The effects of the interface bond layer roughness and pre-crack are focused. The results show that with the increasing roughness of the bonding layer, the extension length of the delamination cracks is reduced. The delamination cracks are suppressed when the roughness increases. The initial vertical TC defects can effectively inhibit the nucleation and extension of the new cracks. This study provides a theoretical foundation for understanding the crack failure mechanism in thermal barrier coatings.

We consider a liquid bridge between identical spheres and present approximate expressions for the capillary force and the exposed surface area of the liquid bridge as functions of the liquid bridge’s total volume and the sphere separation distance. The radius of the spheres and the solid–liquid contact angle are parameters that enter the expressions. These expressions are needed for efficient numerical simulations of drying suspensions and other systems involving liquid bridges whose volume or shape vary in time.

This study examines the influence of zigzag joint configuration on crack propagation in centrally cracked Brazilian disks subjected to diametric forces, employing a 2-dimensional Particle Flow Code (PFC2D). An 80-mm-diameter disk specimen was used, featuring a single zigzag joint positioned at its center. The angles between the zigzag joint walls varied (45°, 90°, 135°), and the angle between loading and joint direction ranged from 0° to 90°. Testing was conducted under Brazilian indirect tensile (Splitting tensile test) conditions, with Acoustic Emission (AE) data utilized to analyze fracture progression. The movements of the boundary rate were kept at 0.005 mm/s. Brazilian tensile strength and uniaxial compression strength of samples were 0.8MPa and 7.4 MPa, respectively. The failure strengths were found to be contingent on the specific failure mechanism, which, in turn, was influenced by the geometric attributes of the flaws considered. The maximum failure force correlated with the number of tensile cracks, which increased as the zigzag notch angle decreased. Initial loading exhibited few AE events, but subsequently, AE hits escalated prior to reaching peak force, with the number of hits increasing as the zigzag notch angle decreased. The failure pattern and maximum force observed in specimens closely mirrored results obtained through both numerical simulations and experimental methods.