Computational Particle Mechanics最新文献

The proportional strain loading test is a prevalent method for investigation diffuse instability. The majority of current research concentrates on narrowly graded materials, with relatively less focus on binary mixtures under proportional strain loading. Therefore, a series of numerical tests have been conducted using the discrete element method to study the influence of fine content and strain increment ratio on the binary mixtures. The test results show that the fine content of binary mixtures is intimately connected to the critical strain increment ratio which precipitate a transition from stability to instability. Binary mixtures characterized by a low stress ratio at the onset of instability also demonstrate a heightened sensitivity to shifts in strain increment ratio. The macroscopic responses, such as the stress ratio at the onset of instability, shear strength, and pore water pressure, exhibit different trends of variation with the fine content compared to microscopic responses, including coordination number, friction mobilization index, and the proportion of sliding contacts. Furthermore, the anisotropy coefficient is introduced to dissect the sources of anisotropy at onset of instability, revealing that strong contact fabric anisotropy can mirror the evolution of the stress ratio. The stress ratio at onset of instability is predominantly influenced by anisotropy in contact normal and normal contact force.

The coupling effect between mixing uniformity and heat transfer of particles in the double barrel with differential velocity (DBDV) was studied. The particle motion model, heat transfer model and their coupled processes were established. The velocity and temperature fields of particles and fluids and the coupling relationship were analyzed. The results indicate that the particle flow direction in the mixing zone is opposite to the fluid flow direction. The velocity and temperature of the fluid are low where particles exist. The velocity and temperature of the fluid closer to the outlet are higher in the mixing zone. The dispersion coefficient decreases with increasing temperature at low and high linear velocities. The dispersion coefficient generally increases with the increase of temperature at medium linear velocity. It is advisable to choose the medium linear velocity to obtain particles with high uniformity and high temperature. This provides theoretical guidance for the development of DBDV.

Understanding the behavior of rock failure under the influence of grain size and temperature is a critical topic in rock mechanics due to its complexity and significance. The impact of these factors, particularly on crack initiation and propagation processes, is a complex and multifaceted issue that has been the focus of engineering rock studies. These effects are especially noticeable when temperature changes drastically, such as deep mining projects or construction in high-temperature regions. Based upon the distinct element method (DEM), this study used the particle flow code (PFC) to numerically simulate the rock fracture process under three-point loading on semi-circular bending (SCB) specimens. A total of 96 fracture toughness tests were simulated on samples with grain sizes of 0.5, 0.75, 1, and 1.5 mm at temperatures ranging from 25 to 700 °C and under mode I, mode II, and mixed-mode fracture loading conditions. The numerical models were validated against uniaxial compressive strength and Brazilian tensile strength test results. This study uniquely examines how temperature and grain size affect crack propagation velocity across different loading conditions. The findings showed that, as temperature increases, microcracks lead to thermal expansion in the samples, and the crack propagation velocity also increases. Additionally, there is an inverse relationship between grain size and crack propagation velocity. Notably, the results showed that the effects of grain size and temperature on crack propagation velocity vary across different fracture modes.

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.