Computational Particle Mechanics最新文献

This research investigates the impact of the brittleness of bedding, bedding angel, and the notch length on the delayed failure and rapid fracturing of notched bedding rock under shear conditions subjected to punch tests. Also, this paper analyzed the acoustic emission events throughout the entire process of rock bridge failure. For this purpose, rectangular two layered samples containing both hard- and soft-rock layers were employed. Each model included two vertical edge notches in a single direction, with notch lengths of 20, 40, and 60 mm. The bedding layers were varied from 90° to − 75° with increments of 15°. The results demonstrate that smooth cracks originated from the notch tip and propagated vertically until coalescing with the upper boundary of the model. The occurrence of acoustic emission in hard, ductile gypsum is considerably greater than that in soft, brittle gypsum. The shear stiffness of bedded rock is maximized when a higher percentage of shear surfaces is occupied by hard and ductile gypsum. Delay failure occurs in the hard, ductile layer, while fast fracturing occurs in the soft, brittle layer. In models with constant notch length, delay failure was occurred in models with a positive layer, whereas fast fracturing was observed in models with a negative layer angle. Additionally, delay failure changes to fast fracturing with an increase in the notch length. Failure patterns, shear stiffness, and shear strengths of the notched bedding models are similar to those of notched physical samples.

The mechanical behavior of rock masses is significantly influenced by the presence of internal holes. This study investigates these effects through uniaxial compression tests and two-dimensional Particle Flow Code (PFC2D) numerical simulations on sandstone samples containing triangular holes with varying apex angles. The results reveal a distinct “W” pattern in both peak strength and elastic modulus as the apex angle increases. For holes with angles less than 60°, cracks preferentially initiated at the apex and propagated along the AB side. In contrast, angles of 60° or greater resulted in crack initiation at the base corners, with damage concentrating along the BC side. This behavior underscores the combined influence of hole area and angular geometry on the strength of the specimens. Acoustic emission monitoring during testing enabled the definition of a damage variable, which was subsequently used to develop a constitutive model based on the Duncan model. The proposed model effectively captures the distinct stages in the stress–strain curves, demonstrating both accuracy and practical relevance.

The performance of graphene–silicon carbide (SiC) composite multilayered structure under various transverse impact loading conditions is considered in this paper. This prototypical system is examined using a multiscale approach which integrates ReaxFF molecular dynamics with Reddy’s third-order shear deformation plate theory in a hierarchical framework. In essence, the developed multiscale analysis combines the simulation of material properties (i.e., graphene nanofiller and the ceramic matrix) at the atomic scale and the mechanics of the structure at the macroscale. Accordingly, the governing equations of the aforementioned system are discretized and solved by utilizing a meshfree method. In that regard, the elastodynamics of such composites is characterized by factoring in constituent materials properties and nanofiller volume fraction. Comprehensive numerical simulations, corroborated by some of the available experimental evidence from the existing reports, reveal that (a) oxidation degree of the graphene nanofiller can be introduced as a novel tuning factor for the elastodynamic response of the macroscale graphene–ceramic composite structures, and (b) higher volume fraction of graphene enhances the flexibility and induces larger deflection of the composite plate under various dynamic loadings (softening effect). Furthermore, the dependency of the results on the structural boundary conditions is assessed. The multiscale approach and findings of this study offer insights into the feasible bottom-up design pathways for developing novel multilayered ceramic matrix composites with graphene inclusion for applications in structural engineering, energy devices, and aerospace industries.

Interlayer cracking has become a major defect in ballastless tracks, and the uniaxial compression behavior and damage under non-coincident interlayer contact have become a key research focus to support service performance. This study establishes a discrete element model for the non-coincident interlayer contact of composite specimens of double-block ballastless track under normal loads. The normal load–displacement curve was obtained, and the meso-damage characteristics with non-coincident interlayer contact were investigated. By analyzing the changes in force chains and crack propagation during the loading process, the damage mechanism of non-coincident interlayer contact is clarified. The influence of roughness on the damage behavior of composite specimens under non-coincident interlayer contact is also discussed. The results show that: 1) The normal displacement increases nonlinearly under normal loads, and during the loading process, the bonding between particles on the rough interface breaks, leading to a sudden drop in load; 2) there is a linear relationship between the number of cracks and displacement in the interlayer region, while in the matrix region, the relationship is stage-dependent. During the stage where damage occurs in both the interlayer interface and matrix, the matrix begins to fail, with 83% of all cracks appearing in this stage; 3) there is a correlation between the force chain and the development of damage in the specimens. When interlayer spalling occurs, shear cracks dominate; when the matrix begins to crack and penetrate, tensile cracks dominate; and 4) the peak strength of specimens with non-coincident interlayer contact and R_a follows an exponential function relationship. As roughness increases, the failure mode of the specimens shifts from primarily matrix cross-penetration to primarily interlayer material spalling. Additionally, the proportion of cracks in the interlayer region relative to the total gradually increases. The results of this study will contribute to a deeper understanding of the damage mechanism after interlayer cracking in ballastless tracks, particularly the damage evolution characteristics at the mesoscopic level.

Before the discrete element method (DEM) is implemented for numerical simulations, the microparameters of the DEM models should be calibrated. Microparameter calibration is a critically important procedure for numerical DEM simulations. The macroparameters obtained from physical tests (e.g. UCS, Young’s modulus, Poisson’s ratio) were used to calibrate the microparameters of DEM models. However, the mechanical characteristics of rock materials cannot be fully reflected by the macroparameters. Hence, in this paper, the stress‒strain relationships of uniaxial compressive tests were used for calibrating the microparameters of DEM (discrete element method) models by using the artificial ecosystem-based optimization (AEO) algorithm, combined with a Python script and a stress‒strain curve of uniaxial compressive tests from laboratory experiments. Additionally, a microparameter calibration framework was proposed. To verify the validity of the proposed method, two examples were evaluated, and the numerical simulation results indicated that the proposed method can be applied to calibrate the microparameters of DEM models. Moreover, to analyse the influence of each microparameter on the stress‒strain curve of uniaxial compressive tests, a large number of numerical simulations were conducted. Finally, based on the analysis, some microparameter calibration suggestions were provided. This study provides a new method for calibrating microparameters and provides calibration suggestions that are critically important for numerical DEM simulations.

Slurry shield construction frequently encounters the risk of air cushion chamber clogging, which may cause pipeline damage at a minor level, or serious abnormal shutdown of the shield machine, resulting in serious negative impacts on construction safety and efficiency. Current studies primarily focus on the transport characteristics of cuttings in the discharge pipe, while the complete process from the air cushion chamber into the discharge pipe until discharge is often overlooked. The air cushion chamber is decisive in this process, fundamentally determining the discharge performance of cuttings. Therefore, the reasonable layout of scouring pipes within the chamber is particularly critical for alleviating the clogging risk. However, the current layout of scouring pipes lacks sufficient guidance, necessitating urgent optimization research. This paper establishes a model that more comprehensively reflects the process of cuttings discharge based on the CFD-DEM method and investigates the effects of scouring pipes layout on cuttings discharge performance. The results indicate that the cuttings discharge performance improves with the decrease in the layout height and rotation angle of the scouring pipes, as well as with the increase in the layout width and extension distance. Additionally, the layout scheme of scouring pipes with optimal discharge performance is determined based on the response surface method. These findings contribute to alleviating the risk of clogging in the air cushion chamber of the slurry shield.

This study developed a numerical model based on the discrete element method to investigate the characteristics of a granular slope-cushion layer during collision. The model considered the influence of cushion particle radius, incidence velocity, cushion thickness, and initial rotational angular velocity. The results indicated that a larger cushion particle radius generated a stronger impact force and a higher percentage increase (up to 34%) in the impact force. The counterclockwise initial angular velocity of the rockfall facilitated the splashing of the cushion particles at the bottom of the slope cushion. The clockwise motion of the rockfall results in its bouncing on the surface of the slope–cushion system. Using the normalization method, the maximum impact force, penetration depth, and energy dissipation ratio were fitted as functions of cushion thickness. The results of this study provide a solid theoretical foundation for the design of slope-cushion layers.

The presented surface indentation model is one step towards building a DEM model for wheel–rail sanding. In railways, so-called low-adhesion conditions can cause problems in traction and braking, and sanding is used to overcome this problem. Sand grains are blasted towards wheel–rail contact, fracture repeatedly as they enter the nip and are drawn into the contact and then increase adhesion. Research on this topic has mostly been experimental, but focussed on adhesion enhancement measurement. Thus, physical mechanisms increasing the adhesion are not well understood. Previous works involved experiments and DEM modelling of single sand grain crushing tests under realistic wheel–rail contact pressures of 900 MPa, focusing on sand fragment spread and formation of clusters of solidified fragments. In the experiments, indents in the compressing steel plates were also observed, which are also observed on wheel and rail surfaces in railway operation. These are now modelled by adapting an existing surface indentation model from literature to the case of surface indentations caused by granular materials. Two test cases are studied, and experimental spherical indentation tests for model parametrisation are presented. In a proof of concept, the mentioned single sand grain crushing tests under 900 MPa pressure are simulated including the surface indentation model. This work contributes to DEM modelling of wheel–rail sanding, which is believed to be a good approach to deepen the understanding of adhesion increasing mechanisms under sanded conditions.