Search Results (48)

This study addresses gas drainage challenges in the Pingdingshan NO.10 mine JI_15-16 coal seam through coupled COMSOL-FLAC^3D numerical simulations. The research evaluates the effectiveness of a cross-measure borehole drainage system. It analyzes the failure mechanisms of the surrounding rock in both the machine roadway and floor roadway of the 24130 working face under the influence of boreholes. The results demonstrate that extended drainage duration progressively reduces both gas content and pressure within the borehole-affected zone of the coal seam while enhancing the effective permeability of the JI_15-16 coal stratum. The operational system extracted 1,527,357 m³ of methane, achieving a pre-drainage efficiency of 59.18% through cross-measure boreholes. The measured gas content aligns with simulated predictions, though field-recorded gas pressure registered slightly higher than modeled values. This validated drainage design complies with the Pingmei Group’s regulations for coal and gas outburst prevention. Critically, cross-measure boreholes alter stress distribution around both coal and floor roadways, promoting plastic zone expansion. Consequently, during the development of the 24130 working face’s machine roadway, intensified ground pressure monitoring is essential near borehole locations in the roof, floor, and rib strata. Supplementary support reinforcement should be implemented when required to prevent rib spalling and roof collapse incidents. Full article

Crack initiation, propagation, and slippage serve as the key mesoscopic mechanisms contributing to the deterioration of deep tunnel surrounding rocks. In this study, a secondary anisotropy of deep tunnels surrounding rocks was proposed: The axial-displacement constraint of deep tunnels forces cracks in the surrounding rock to initiate, propagate, and slip in planes parallel to the tunnel axial direction. These cracks have no significant effect on the axial strength of the surrounding rock but significantly reduce the tangential strength, resulting in the secondary anisotropy. First, the secondary anisotropy was verified by a hybrid stress–strain controlled true triaxial test of sandstone specimens, a CT 3D (computed tomography three-dimensional) reconstruction of a fractured sandstone specimen, a numerical simulation of heterogeneous rock specimens, and field borehole TV (television) images. Subsequently, a novel SSA (strain-softening and secondary anisotropy) constitutive model was developed to characterise the secondary anisotropy of the surrounding rock and developed using C++ into a numerical form that can be called by FLAC^3D (Fast Lagrangian Analysis of Continua in 3 Dimensions). Finally, effects of secondary anisotropy on a deep tunnel surrounding rock were analysed by comparing the results calculated by the SSA model and a uniform strain-softening model. The results show that considering the secondary anisotropy, the extent of strain-softening of the surrounding rock was mitigated, particularly the axial strain-softening. Moreover, it reduced the surface displacement, plastic zone, and dissipated plastic strain energy of the surrounding rock. The proposed SSA model can precisely characterise the objectively existent secondary anisotropy, enhancing the accuracy of numerical simulations for tunnels, particularly for deep tunnels. Full article

The instability of mine roadways is significantly influenced by the coupled effects of groundwater seepage and non-uniform loading. These interactions often induce localized plastic deformation and progressive failure, particularly in the roof and sidewall regions. Seepage elevates pore water pressure and deteriorates the mechanical properties of the rock mass, while non-uniform loading leads to stress concentration. The combined effect facilitates the propagation of microcracks and the formation of shear zones, ultimately resulting in localized instability. This initial damage disrupts the mechanical equilibrium and can evolve into severe geohazards, including roof collapse, water inrush, and rockburst. Therefore, understanding the damage and failure mechanisms of mine roadways at the mesoscale, under the combined influence of stress heterogeneity and hydraulic weakening, is of critical importance based on laboratory experiments and numerical simulations. However, the large scale of in situ roadway structures imposes significant constraints on full-scale physical modeling due to limitations in laboratory space and loading capacity. To address these challenges, a straight-wall circular arch roadway was adopted as the geometric prototype, with a total height of 4 m (2 m for the straight wall and 2 m for the arch), a base width of 4 m, and an arch radius of 2 m. Scaled physical models were fabricated based on geometric similarity principles, using defect-bearing sandstone specimens with dimensions of 100 mm × 30 mm × 100 mm (length × width × height) and pore-type defects measuring 40 mm × 20 mm × 20 mm (base × wall height × arch radius), to replicate the stress distribution and deformation behavior of the prototype. Uniaxial compression tests on water-saturated sandstone specimens were performed using a TAW-2000 electro-hydraulic servo testing system. The failure process was continuously monitored through acoustic emission (AE) techniques and static strain acquisition systems. Concurrently, FLAC^3D 6.0 numerical simulations were employed to analyze the evolution of internal stress fields and the spatial distribution of plastic zones in saturated sandstone containing pore defects. Experimental results indicate that under non-uniform loading, the stress–strain curves of saturated sandstone with pore-type defects typically exhibit four distinct deformation stages. The extent of crack initiation, propagation, and coalescence is strongly correlated with the magnitude and heterogeneity of localized stress concentrations. AE parameters, including ringing counts and peak frequencies, reveal pronounced spatial partitioning. The internal stress field exhibits an overall banded pattern, with localized variations induced by stress anisotropy. Numerical simulation results further show that shear failure zones tend to cluster regionally, while tensile failure zones are more evenly distributed. Additionally, the stress field configuration at the specimen crown significantly influences the dispersion characteristics of the stress–strain response. These findings offer valuable theoretical insights and practical guidance for surrounding rock control, early warning systems, and reinforcement strategies in water-infiltrated mine roadways subjected to non-uniform loading conditions. Full article

Incorporation of plastic waste into concrete mitigates harm to the environment through encapsulation of plastics in concrete. This study presents a comprehensive investigation of the effects of using six commonly used plastic materials (i.e., polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS)) in cement paste and mortar mixtures. The heat of hydration investigations revealed that plastic powders did not significantly affect rates or extents of hydration. Among the different types of plastic-aggregate mortars, PET performed the worst, while PS was the best. Fractures in the samples generally occurred due to debonding between the plastic particles and the cement matrix. Plastic particle shape influences the microstructure of the interfacial transition zone and consequently affects the overall strength of the mortar. Full article

This study develops a new physical and analytical model for the particle scratching process, where a particle is modeled as a sphere. It investigates the flow of workpiece material introduced by the particle’s motion, dividing the contact area into zones of elastic and plastic deformation. Forces applied to the particle in both zones are calculated, and parameters defining the extent of elastic rebound and plastic upheaval are introduced. The study also presents stress distribution in the plastic zone, discusses the factors influencing the force ratio, and reveals that the force ratio increases with greater elastic rebound, plastic upheaval, cutting depth, and strain strengthening, but decreases with larger particle sizes. Yield stress was found to have no effect on the force ratio. These findings will guide research in practical material processing as well as in scratch applications. Full article

Deep-buried subsea tunnels are often under high water pressure conditions, and the influence of the seepage field on the tunnel cannot be ignored. Existing studies generally assume that the surrounding rock exhibits permeability isotropy; this study developed a model of deep-buried subsea tunnel that considers the permeability anisotropy of surrounding rock and investigated the effects of permeability differences between the surrounding rock and lining structure on tunnel seepage flow and plastic zone extent. By employing coordinate transformation and conformal mapping methods, the hydraulic head and the seepage discharge for each region are determined for each section of the tunnel. Based on the analytical solution of the seepage field, the seepage force is treated as a body force, and using the Mohr–Coulomb criterion, an elastoplastic analytical solution for the lining and surrounding rock under anisotropic seepage is derived. Using the Shenzhen MaWan Sea-Crossing Passage as a case study, numerical simulations are conducted using Abaqus2021, and the results are compared with the analytical solution to verify the accuracy of the study. The research shows that the permeability anisotropy of surrounding rock increases the seepage discharge, and this effect becomes more significant with increasing burial depth. If the anisotropy is 10 times greater than its previous value, the tunnel seepage volume will increase by 35.6%. When the surrounding rock permeability is sufficiently large, the impact of permeability anisotropy on the seepage discharge is relatively weak, with the seepage discharge primarily dominated by the permeability of the lining. In the tunnel stress field, due to the significant difference in stiffness between the lining and the surrounding rock, the hoop stress in the lining is much larger than that in the surrounding rock, and there is a stress discontinuity at their interface. When the permeability of the elastic zone of the surrounding rock is 100 times greater than that of the plastic zone, the plastic radius of the tunnel will increase by 2 to 3 times compared to the previous value. Reducing the permeability of the plastic zone in the surrounding rock effectively limits the seepage body force acting on the lining, thereby enhancing the stability of the lining structure and reducing the risk of damage to the tunnel. Full article

Titanium alloys find extensive applications in aviation, maritime, and chemical engineering applications. Nonetheless, these alloys encounter significant challenges during the conventional forging process, which include high deformation resistance, limited processing temperature ranges, and inhomogeneous microstructure. Isothermal forging, as a near-net-shape forming technique, can alleviate the microstructural inhomogeneity caused by deformation dead zones in conventional forging, thus enabling the direct production of complex shapes. This process enhances the overall performance and utilization of materials while reducing manufacturing costs. This paper comprehensively reviews how isothermal near-net-shape forging process parameters influence the intricate microstructure and essential properties of titanium alloys. The unique properties of isothermal forging applied to high-performance titanium alloys are also discussed in depth, and the intricate interplay between process parameters and the microstructure and properties of recoloration is clarified. That is to say, temperature is a vital element influencing the phases and microstructure of titanium alloys during the forming process. Grain size, microstructural homogeneity, and phase transformation are influenced by the strain rate, thereby affecting the plasticity, fracture toughness, and strength of titanium alloys. The extent of deformation significantly governs the grain size, the thickness of secondary α phase, dynamic recrystallization, and primary α phase. Cooling rate affects the grain size and precipitates, contributing to grain refinement. The frequency of isothermal forging affects the grain refinement and microstructural uniformity of titanium alloys. Finally, this paper summarizes the scientific questions that remain unresolved in this field and outlines future research directions to promote the further development of isothermal near-net-shape forging processes and facilitate the broader industrial applications of high-performance titanium alloys and other difficult-to-form alloys. Full article

Aiming to address the challenges of determining the coal pillar’s width and managing the significant deformation of the surrounding rock in the deep gob-side entry driving, the limiting equilibrium zone theory, employing the operational area of Dongpang Mine 21110 as the engineering setting, states that a coal pillar’s appropriate width in the gob-side entry driving falls between 7.9 and 9.8 m. The pattern of vertical stress distribution and the extent of the plastic zone in the roadway for coal pillar widths of 7.0 m, 8.0 m, 9.0 m, and 10.0 m are analyzed, respectively, investigated using the numerical simulation method of FLAC^3D. The acceptable coal pillar width in the deep gob-side entry driving is 8.0 m. Combined with the roadway surrounding rock borehole inspection results, the fracture development condition of the roadway’s full-face surrounding rock is determined, and the asymmetric aberration characteristics, with significant surrounding rock damage depth at the coal pillar flank location, are obtained. Based on the theoretical calculations, an integrated proposal for a “non-symmetrical bolt and cable anchor” coupling support scheme for the surrounding rock in the gob-side entry driving is put forward. This was applied at the Dongpang coal mine site. Engineering practice shows that leaving an 8.0 m coal pillar width and adopting the “non-symmetrical bolt and cable anchor” support system design can control the deformation of the surrounding rock in the track entry at a reasonable range, which ensures the stability of the surrounding rock in the gob-side entry driving. Full article

Investigating deformation and failure mechanisms in shafts and roadways due to rock subsidence is crucial for preventing structural failures in underground construction. This study employs FLAC^3D software (vision 5.00) to develop a mechanical coupling model representing the geological and structural configuration of a stratum–shaft–roadway system. The model sets maximum subsidence displacements (MSDs) of the horsehead roadway’s roof at 0.5 m, 1.0 m, and 1.5 m to simulate secondary soil consolidation from hydrophobic water at the shaft’s base. By analyzing Mises stress and plastic zone distributions, this study characterizes stress failure patterns and elucidates instability mechanisms through stress and displacement responses. The results indicate the following: (1) Increasing MSD intensifies tensile stress on overlying strata results in vertical displacement about one-fifth of the MSD at 100 m above the roadway. (2) As subsidence increases, the disturbance range of the overlying rock, shaft failure extent, and number of tensile failure units rise. MSD transitions expand the shaft failure range and evolve tensile failure from sporadic to large-scale uniformity. (3) Shaft failure arises from the combined effects of instability and deformation in the horsehead and connecting roadways, compounded by geological conditions. Excitation-induced disturbances cause bending of thin bedrock, affecting the bedrock–loose layer interface and leading to shaft rupture. (4) Measures including establishing protective coal pillars and enhancing support strength are recommended to prevent shaft damage from mining subsidence and water drainage. Full article

The material flow behavior during friction stir welding (FSW) plays a critical role in the quality of final joints. In this study, the FSW of LAZ931 duplex Mg alloy was carried out at a rotation speed of 800 rpm and welding speeds of 50, 100, and 200 mm/min, respectively. A thin pure Mg strip inserted at the interface between the two Mg-Li alloy plates was used as a marker to study the flow behavior of the materials in the FSW process. Sound welds with no defects were obtained for all three welding speeds. The microstructural evaluations along the marker on the horizontal cross-section around the keyhole of the welds were characterized. As the welding speed increased, the marker came closer to the keyhole, indicating the decreased extent of the plastic deformation of the material. In the shoulder-affected zone (SAZ), the thickness of the marker reduced gradually in the accelerating stage and finally accumulated together in the decelerating stage. However, in the pin-affected zone (PAZ), the thickness of the marker reduced sharply in the accelerating stage and then became dispersed in the decelerating stage, and the degree of dispersion decreased as the weld speed increased. As a result, an elongated grain structure was formed in the SAZ, while two equiaxial grain structures were formed in the PAZ. The material on the advancing side was refined by the pin and deposited in the weld to form a fine equiaxial grain structure due to the high strain rate. In contrast, the material on the retreating side was pushed by the pin and thus directly deposited in the weld to form a coarse equiaxial grain structure. In addition, the area of the fine equiaxial grain structure was reduced obviously with the increase in welding speed. Full article

The stability of salt cavern storage during prolonged operation is a crucial indicator of its safety. This study focuses on an operational underground gas storage facility, conducting comparative numerical simulations for the storage of natural gas and hydrogen. We investigated the evolution of stability for natural gas and hydrogen storage under long-term storage conditions. The main conclusions are as follows: (1) A new equation for stress equilibrium and constitutive relations are derived. (2) At the same storage pressure, the effective stress at the same position in the interlayer is greater for hydrogen storage compared to natural gas storage, signifying a higher level of danger. (3) At the same storage pressure, the displacement at the cavity top for hydrogen storage is greater than that for natural gas storage. The displacement difference between the two is greatest at 9 MPa, amounting to 0.026 m. (4) Due to hydrogen’s lower dynamic viscosity and higher permeability, the depth and extent of the plastic zones within the interlayers are greater compared to natural gas. When the storage pressure is 15 MPa, the depth of the plastic zone within the interlayer can be up to 2.1 m greater than when storing natural gas, occurring in the third interlayer from the top. These research findings may serve as a valuable reference for determining the operational parameters of on-site salt cavern hydrogen storage facilities. Full article

The extent of the plastic zone is critical in determining the stability and extent of damage to the surrounding rock in tunnels, crucial for designing support structures and thermal insulation layers. This study focuses on understanding how rock thermal stress affects the expansion of the plastic zone in deep-buried tunnels subjected to high geothermal temperatures, based on the derivation of the boundary line formula of the plastic zone in a high geothermal tunnel, and combined with the test results of the hydraulic fracturing method in a high geothermal tunnel of the Bulunkou Hydropower Station in Xinjiang. The findings indicate that thermal stress in the rock mass slows the growth of the plastic zone but significantly increases its extent. However, the influence of thermal stress on the shape and size of the plastic zone is less significant compared to the lateral pressure coefficient. In conditions of high geothermal temperature and geostress, rock mass thermal stress induces substantial changes in the morphology and extent of the plastic zone, which cannot be overlooked and can lead to significant errors if not properly considered. The theoretical formulas derived from engineering analysis, along with observed patterns of plastic zone expansion, demonstrate practical applicability. Full article

Mg-Gd-Y-Zn-Mn (MVWZ842) is a kind of high rare earth magnesium alloy with high strength, high toughness and multi-scale strengthening mechanisms. After heat treatment, the maximum tensile strength of MVWZ842 alloy is more than 550 MPa, and the elongation is more than 5%. Because of its great mechanical properties, MVWZ842 has broad application potential in aerospace and rail transit. However, the addition of high rare earth elements makes the deformation resistance of MVWZ842 alloy increase to some extent. This leads to the difficulty of direct plastic processing forming and large structural part shaping. Friction stir welding (FSW) is a convenient fast solid-state joining technology. When FSW is used to weld MVWZ842 alloy, small workpieces can be joined into a large one to avoid the problem that large workpieces are difficult to form. In this work, a high-quality joint of MVWZ842 alloy was achieved by FSW. The microstructure and properties of this high-strength magnesium alloy after friction stir welding were studied. There was a prominent onion ring characteristic in the nugget zone. After the base was welded, the stacking fault structure precipitated in the grain. There were a lot of broken long period stacking order (LPSO) phases on the retreating side of the nugget zone, which brought the effect of precipitation strengthening. Nano-α-Mn and the broken second phase dispersed in the matrix in the nugget zone, which made the grains refine. A relatively complete dynamic recrystallization occurred in the nugget zone, and the grains were refined. The welding coefficient of the welded joint exceeded 95%, and the hardness of the weld nugget zone was higher than that of the base. There were a series of strengthening mechanisms in the joint, mainly fine grain strengthening, second phase strengthening and solid solution strengthening. Full article

The collapse of thick-hard roofs after coal has been extracted is not a consequential process in all cases. Rather, it happens due to the augmentation of high stress conducted at depth, followed by a wider range of damage as the floor cracks. The extent and spread of the cracks in the floor indicate the intensity of the collapse, and the mine will be submerged by the high-pressure water of the coal ash. Therefore, it is particularly important to study the mechanism of the combined effect of high stress on the roof and confined aquifer on the deformation and failure of the coal seam mining floor. This study analyzes and compares the impact of thick-hard magmatic rocks on the destruction of thin floor rock layers in coal seams. Plastic theory calculations are used to determine the plastic zone yield length of floor destruction under hard roof conditions, and the location and height of the maximum floor destruction depth are solved. An empirical formula and BP neural network are used to establish a prediction model for floor destruction. The results of the model’s prediction of the depth of floor failure were compared with the measured values, with an absolute error of 2.13 m and a residual of 10.3%, which was closer to the true values. The accuracy of the theoretical model and prediction model is verified using numerical simulation and on-site in situ measurements. Based on this, the deformation and destruction forms of the floor under pressure and the water inrush mechanism are summarized for mining under the condition of a thick-hard roof. Thus, the floor is subjected to high vertical stress, accompanied by significant disturbances generated during coal seam mining, resulting in intense working face pressures. The floor near the working face coal wall will experience severe compression and shear deformation and slide towards the goaf. The floor in the goaf is relieved of high vertical stress, and horizontal stress compression will result in shear failure, leading to floor heave and further increasing the height of the floor destruction zone. After the mining of the working face, the goaf will undergo two stages of re-supporting and post-mining compaction. During the re-supporting stage, the floor rock undergoes a transition from high-stress to low-stress conditions, and the instantaneous stress relief will cause plastic deformation and failure in the coal seam floor. The combined action of primary floor fractures and secondary fractures formed during mining can easily create effective water channels. These can connect to the aquifer or water-conducting structures, making them highly dangerous. The main modes of floor water inrush under the condition of a thick-hard roof are as follows: the high-stress mode, inducing a floor destruction zone connected to the water riser zone; the mining damage mode, connecting to water-conducting faults; the mining damage mode, connecting to water collapse columns; and the coupled water inrush mode, between the mining damage zone and the highly pressurized water floor. Full article

There are some important advantages presented by metal specimens coated with WIP-C1 (Ni/CrC)-type materials. However, given the coating methods and the stress under dynamic loads, there are issues that need to be taken into account, particularly in terms of the behavior at the interface between the two materials. Using standardized cylindrical 1018 steel specimens uniformly coated with WIP-C1 (Ni/CrC) by cold spraying, this study investigated the fatigue behavior of the specimen as a whole, focusing on the interface areas of the two materials. The fatigue life diagram is given, to a large extent, by the behavior of the base material. As a result, in this work, we have focused not so much on the fatigue behavior of the assembly as on the integrity of the coating material and the defects, failures, etc., that may occur at the interface after a certain number of cycles. The applied load was cyclic fatigue through alternating–symmetric cycles. Scanning optical microscopy was used to observe plastic deformations and crack propagation during the breakage process. It was found that both the base material zone and the cover material zone presented good performance when the maximum stresses were at low values. A fatigue durability curve was also plotted, showing a conventional appearance for a metallic material, slightly influenced by the destruction of the base material interface. At higher maximum stress and, consequently, to large strains, a series of destructions at the interface of the two materials, of different types, were observed and will be highlighted in the paper. Full article