Computational Particle Mechanics最新文献

Hydraulic fracturing is a pivotal technology for enhancing reservoir permeability and is extensively utilized in the production of coal seam gas. In soft coal seams, drilling operations can precipitate coal and gas blowouts, forming a cavity at the base of the drill hole. However, the effect of this cavity on the initiation and propagation of hydraulic cracks remains inadequately understood. This study employs the discrete element method in conjunction with the acoustic emission moment tensor algorithm to investigate how the cavity angle α impacts fracture propagation. The findings indicate that an increase in cavity angles correlates with a rise in the number of branch fractures observed, due to the increase in the projection area S_h of the cavity in the minimum horizontal principal stress direction. Additionally, as the cavity angle increased, there was a noted increase in initiation pressure and the statistical magnitude of acoustic emission events. Moreover, the spatial distribution fractal dimension D of acoustic emission events logarithmically increased with α. The b value of acoustic emissions escalated with α, reaching its maximum at α = 60°, where the stimulated influence area was maximized. These findings suggest that cavity-shaped holes can significantly enhance the complexity of hydraulic fractures, thereby facilitating a more extensive fracture network within coal seams, which is crucial for effective gas extraction.

A novel two-stage mining method, involving large-height mining of the medium layer followed by top-coal caving in the lower layer, has recently been applied to extremely thick coal seams (> 20 m). Throughout the mining process, the top-coal layer undergoes two distinct stages of disturbance and failure, influenced by multiple factors that impact mining efficiency. Based on geological conditions in western China, this study employs numerical simulations to analyze the impact of coal seam burial depth, medium layer thickness, and its location on top-coal movement and pressure distribution under high-intensity repeated mining. The results reveal the formation of a strip-like stress zone and a wide-bottomed inverted funnel displacement field in the top-coal layer during medium layer mining, with maximum stress and subsidence reaching approximately 34.7 MPa and 3 m, respectively. During the lower layer mining stage, crack propagation and coal fragmentation enhance top-coal caving, forming a sawtooth-shaped displacement boundary. Additionally, maximum top-coal subsidence increases to 5.3–7.3 m as burial depth and medium layer mining height increase. These findings suggest that initiating the first mining face in the middle-lower section of the coal seam, where top-coal stress is highest, promotes efficient coal breakage and smooth caving.

The utilization of hydraulic fracturing technology to create an intricate network of hydraulic fractures in hard rocks to improve its cuttability, subsequently followed by the non-explosive mechanized mining through tunnel boring machines, is poised to emerge as a novel production paradigm for hard rock mines. In this study, a discrete element model of mechanized mining assisted by hydraulic fracturing techniques for hard rock cutting was established, and the evolution characteristics of the peak cutting force (PCF) of rock cutting recorded by drill bit after hydraulic fracturing were explored under various variables. Based on this, the hydraulic fractures recognition system was developed, wherein the hydraulic fractures network was projected onto the X/Y axis. The results demonstrate that the distance between the pressure hole and the top boundary (DT) is an important factor influencing the average cutting force of rock. Furthermore, a significant improvement in cuttability is observed at DT = 50 mm. Among all variables, the angle of guiding groove in double hole (DGA) has the most significant impact on rock cutting. When DGA = 20°, the PCF reaches the lowest value among all variables, and the hydraulic fractures are regarded as the ideal morphology of hydraulic fracture network under all variables. In terms of its longitudinal projection distribution, hydraulic fractures generate a central projection and gradually diminishes to zero pixels on both sides. Horizontally, the hydraulic fracture is distributed all over the horizontal direction of the rock, resulting in a double-peaked projection distribution at the two pressure holes.

Underground hydrogen storage (UHS) is an important way to alleviate the fluctuating renewable energy production. But the hydrogen embrittlement affects the efficient and safe operation of UHS. In this study, a peridynamic plastic hydrogen embrittlement model (PDPHE model) is developed to analyze the hydrogen-related damage of the UHS. The proposed PDPHE model can capture the full process of the hydrogen-assisted crack propagation, including the crack initiation and the crack propagation. The influences of hydrogen diffusion and plastic deformation on the damage nucleation are considered in the proposed model. To improve the computing efficiency, parallel computing is applied in the numerical simulation by using the CUDA framework from the NVIDIA. The numerical examples investigate the hydrogen-assisted crack propagation of mode I and the complex mode. The validity and the efficiency of the proposed PDPHE in simulating the damage caused by the hydrogen embrittlement effect are validated. The hydrogen-related damage of the UHS casing pipe is numerically analyzed. And the numerical results indicate that the applied load and the initial applied hydrogen concentration have an impact on the crack nucleation and the propagation speed.

The rock bolt–grout interface (BGI) represents the weakest link in anchorage systems. Under cyclic loading, continuous slip and closure at the interface lead to degradation of its load-bearing capacity and fatigue damage. To investigate the fatigue shear behavior of the BGI, laboratory shear tests were conducted to provide a basis for calibrating the mechanical parameters in simulations. Subsequently, a series of numerical simulations of cyclic shear on the BGI were performed. The number of cracks increased in a stepwise manner over time, initially concentrated on the left side of the BGI and then gradually extending to the right, ultimately resulting in through-cracks. High frequency, high amplitude, and high stress levels accelerated crack extension, weakening the bonding strength at the BGI. The introduction of irreversible strain for a quantitative analysis of the fatigue process revealed that increases in frequency, amplitude, and maximum shear stress levels significantly accelerated damage accumulation and shortened fatigue life. Additionally, the direct shear test with an amplitude of 0 revealed creep characteristics, with initial shear displacement increasing steadily before accelerating due to damage accumulation. Fitting analysis indicated that increases in frequency, amplitude, and maximum shear stress level significantly raised the initial shear displacement and accelerated its growth rate.

The cemented body formed by cement-based materials and crushed stone after cementing is a brittle material, and the content and particle sizes of the crushed stone cause the specimens to show different damage patterns. In order to quantitatively study the effect of crushed stone content and particle sizes on the strength of cemented bodies, in this paper, crushed stone cemented body (CSCB) were prepared using crushed stone (CS), aluminate cement (AC), fly ash (FA), alkali-activated. The real shape of crushed stone was obtained and the numerical model was constructed using 3D scanning modeling, the fine-scale parameters of the PFC numerical model were calibrated and calibrated according to the experimentally measured stress–strain curves, and a series of specimens were constructed for crushed stone content and crushed stone particle sizes. The uniaxial compressive strength, crack extension and distribution pattern, high and low stress force chain distribution, and contact force fabric characteristics of specimens with different crushed stone content and crushed stone particle sizes under the same axial loading conditions were investigated. The results show that (1) the strength of the specimen and the total number of cracks produced by the specimen show a negative correlation, the distribution of internal cracks in the specimen with high strength is concentrated and dominated by one main crack with a lower total number of cracks, and the number of cracks in the specimen with low strength is higher and the distribution is dispersed. The development and expansion of cracks is the main reason for the final destruction of the cemented body. (2) The internal contact forces are redistributed after the specimen is loaded, and the number of high stress force chains accounted for determines the compressive strength of the specimen. With the increase in crushed stone content, the strength shows a first increase and then decrease. (3) Crushed stone content in the range of 50–60% contributes the most to the strength of the specimen. The effect of crushed stone particle sizes on the strength is more complicated, the strength of crushed stone cemented body of 3–5 mm and 5–7 mm particle sizes is larger, and the effect of contact between cement and crushed stone is good, and the effect of internal cement and crushed stone cementation is poor in the specimens with particle sizes of 6–8 mm and 7–9 mm.

Fiber characterization is a major challenge in conventional peridynamic (PD) simulations since the regular discretized grid restricts the direction of bond-pairs between material points. In this work, a new computational model for composite materials with arbitrary fiber orientations (AFOM) is proposed to extend the application scope of conventional PD models in engineering structures. In order to match the practical carbon fiber structure, the fiber bond is analyzed as a special type of research object in AFOM. The most unique feature is that two types of material points are utilized to model a composite structure, and a mapping relation is proposed to achieve data exchange for these component materials. Thanks to this operation, the developed AFOM can remove the limitation of conventional bond-based or ordinary state-based PD in terms of reinforcement characteristics, and the deformation and progressive damage behaviors of composite materials with general fiber orientations can be easily captured. It has been demonstrated from the deformation examples that the proposed AFOM can describe the anisotropic properties of composite structures with general layups well. The damage examples of composite laminates further demonstrate that the proposed AFOM can adaptively replicate the failure characteristics of anisotropic materials without any theoretical limitations.

The stability of the hole-bolt composite structure (HBCS) is crucial for controlling the surrounding rock in engineering. Based on the experimental results, the discrete element analysis was employed to investigate the fracture properties and collaborative mechanism of HBCS. Initially, the theoretical analysis indicates that the stress within the surrounding rock around the pressure relief hole is influenced by the rock mass’s properties and the spatial distance. The mechanical response observed in the models is consistent with the results from physical tests. Observations of fracture suggest that a higher bolt pre-tightening force promotes the coalescence of tensile cracks between the hole and bolt. In contrast, increased hole-bolt spacing leads to more discontinuous cracks. Data monitored using measuring balls show that the stress around the pressure relief hole initially increases as hole-bolt spacing rises, while it will diminish on the upper and horizontal sides of the hole. Furthermore, stress nephograms illustrate a proportional relationship between the stress around the bolt and the bolt pre-tightening force, with an expanding low-stress area occurring as hole-bolt spacing increases. The variations in bolt force further corroborate that larger hole-bolt spacing enhances the reinforcement capacity of the bolt. These findings demonstrate that the hole-bolt collaborative mechanism enables the bolt to achieve optimal reinforcement effectiveness, while maximizing the pressure relief capabilities of the pressure relief hole, thereby enhancing the strength and stiffness of the HBCS. This research provides critical insights for controlling the stability control of surrounding rock in high-stress roadways.

This research proposes an algorithm to produce two ellipses in 2D, or two ellipsoids in 3D, of known major and minor axis lengths, relative orientations, and known separation/penetration distance. More precisely, the parameters describing the pair are exactly satisfied and the distance is observed to be close to the desired order of magnitude. The algorithm can be used to test and compare contact detection algorithms, or to produce large samples of pairs of ellipses and ellipsoids with known statistical properties.

Random joints are the most common defects in rock mass. Joint size or number seriously affects the stability of rock mass. To study the effects of random joints on the mechanical properties and failure characteristics of rock mass, rock-like specimens and numerical models containing random joints were prepared and constructed, and laboratory and numerical uniaxial compression tests were both carried out. The experimental and simulation results show that as the joint size or number increases, the compressive strength of specimen or model decreases in a cubic polynomial curve, the elastic modulus decreases slightly in a straight line, and the fracture growth degree increases linearly. Joint size or number has significant effect on crack initiation and growth. Cracks initiate at the place of joint intersection and concentration and expand into macro-fracture surface. Tensile cracks are the main crack type during the compression process, the number of tensile cracks account for more than 80%, and this proportion increases with increasing joint size or number, while shear cracks only increase significantly after peak stress. Increasing joint size or number reduces the CI stress, and advances the initiation, propagation and intersection of cracks. The influence of joint size or number on mechanical properties and crack propagation is similar, but the influence of joint size is greater. The failure mode is tension-shear coupling failure, but tensile failure is the main one. The results can provide reference for stability analysis and safety assessment of jointed rock mass.