Based on microstructure analysis, diffusion theory, and hot deformation experiments, the solidification microstructure and element segregation of the Alloy 625 Plus ingot, the diffusion kinetics of Ti, Nb, and Mo during homogenization and the hot deformation behavior of the homogenized ingot were investigated in this study. The results indicate that: (1) the solidified ingot exhibits a typical dendritic microstructure, and significant element segregation occurs, leading to the presence of Ti, Nb, and Mo-rich precipitates in the interdendritic region; (2) Following homogenization, the degree of element segregation in the ingot is significantly reduced. The diffusion coefficients (D) of Ti, Nb, and Mo under various homogenization conditions were calculated. Subsequently, the diffusion constants (D0) and activation energies (Q) of Ti, Nb, and Mo were obtained to be 0.01432, 0.00397 and 0.00195 cm2/s and 244.851, 230.312, and 222.125 kJ/mol, respectively. Finally, the diffusion kinetics formulas for Ti, Nb, and Mo in Alloy 625 Plus were established. After homogenization at 1220 °C for 8 h, the alloy exhibits low deformation resistance, a high degree of recrystallization, and optimal deformation coordination ability. Therefore, this represents a rational single-stage homogenization process.
The effects of nanosecond laser shock peening without coating (LSPwC) and nanosecond stacked femtosecond laser shock peening compound strengthening (LSP-CS) on the surface integrity and fretting fatigue lifetime at 500 °C of GH4169 dovetail component were investigated. The results show that LSP treatment does not significantly lead to changes in the grain size of GH4169 alloy, but it introduces a large number of dislocations, resulting in the formation of a plastic deformation layer and residual compressive stress layer. The surface microhardness increased by 20.5% and 28.6% after being treated by LSPwC and LSP-CS, respectively. The surface residual compressive stresses were (−306.5±42.5) MPa and (−404.3±34.7) MPa, respectively; The depth of both the hardening layer and the residual compressive stress layer is 400 µm, and along the cross-section with 0–100 µm region after LSP-CS treatment has higher hardness and greater residual compressive stress. The fretting fatigue lifetime of the GH4169 dovetail component at 500 °C was increased by 346.8% and 494.9%, which is the result of the combined effects of the hardening layer and the residual stress layer. The LSP-CS treatment can effectively make up for the disadvantage of the LSPwC treatment, and further enhance the fretting fatigue lifetime of the GH4169 dovetail component at high temperature.
It is of great significance to study the corrosion process of aluminum (Al) alloys fasteners in order to mitigate corrosion for their widespread applications. In this paper, a method for enhancing the corrosion resistance of Al alloy fasteners is proposed. 7075 Al alloy parts with a fine-grained microstructure were prepared by pre-heat treatment (PHT), combined subsequent equal channel angular pressing (ECAP) and cold upsetting (CU). The corrosion behavior of the specimens was investigated by intergranular corrosion and electrochemical test. Microstructure investigations were carried out by field emission scanning electron microscopy, energy dispersive spectrometer and transmission electron microscopy. The relationship between microstructural evolution and corrosion resistance changes was also explored. The results show that both PHT and ECAP-CU significantly improved the corrosion resistance of the samples and modified the corrosion process. The open circuit potential, corrosion current density and corrosion rate of the alloy on electrochemical test were (−0.812±8.854)×10−5 V (vs. SCE), (6.379±0.025)×10−6 A/cm2 and 0.066 mm/year, respectively, and the intergranular corrosion depth was (557±8) µm. The main factor controlling the corrosion behavior was the microstructure evolution. After PHT, the disappearance of the dendritic structure and the dissolution of the nonequilibrium second phase eliminated the potential difference between the phases, reducing the free energy in the as-cast state. When ECAP-CU was used after PHT, the grain refinement was accompanied by a high density of grain boundaries and dislocations, which led to the formation of a denser passivation film on the alloy surface, improving the corrosion resistance in an aggressive environment.
Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications. The microstructure and corrosion behavior of AZ31Mn-xEr (x=0.1, 0.5, 1.2) alloys were systematically investigated using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), combined with Tafel polarization and electrochemical impedance spectroscopy (EIS) analyses. The findings showed that the alloying element Er refined the grain structure during solidification by increasing the nucleation rate and forming a secondary phase of Al3Er with Al. The Er and Mg in the matrix co-oxidize to form a dense MgO/Er2O3 composite oxide, preventing the formation of loose magnesium hydroxide/basic magnesium carbonate. The trace alloying element Mn interacts with impurities Fe in the magnesium matrix to form an AlFeMn second phase, reducing micro-galvanic corrosion driving force. Electrochemical testing in a 3.5% NaCl solution demonstrated a marked reduction in corrosion rate from 10.46 mm/a (AZ31Mn alloy) to 0.44 mm/a (AZ31Mn-1.2Er alloy). This research offers a reference for searching for corrosion-resistant magnesium alloy and degradable medical magnesium alloy materials.
In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils, nanocrystalline Ni foils with different grain thickness-to-grain size ratios (λ) were prepared using pulsed electrodeposition in this paper and unidirectional tensile experiments were carried out at room temperature with different currents and their applied directions. The experimental results show that the nanocrystalline Ni foil produces an obvious electroplasticity effect after applying the current field, and when 300< λ <1100, the current weakens the size effect of nanocrystalline Ni foils to a certain extent, and the angle between the current direction and the deformation direction also affects the mechanical response of nanocrystalline Ni foils, and when the angle between the current direction and the deformation direction is 0°, electroplasticity effect is the best, and the current has the most significant effect of abating the size effect of the material. The mechanism of unidirectional tensile deformation of nanocrystalline Ni foils under the effect of pulsed current was analyzed using TEM and TKD. It was found that the applied pulse current increased the activity of the nanocrystalline boundaries, promoted the movement of dislocations, and reduced the tendency of dislocation entanglement. The higher the peak current density and the smaller the angle between the direction of the current and the direction of deformation, the smaller the grain boundary orientation difference, the more dispersed the grain orientation, and the lower the density of geometrically necessary dislocations (GND) in the deformed nanocrystalline foil, the more significant the effect on material plasticity improvement.
Electroshocking treatment (EST), an efficient and rapid material treatment method, promotes microstructure evolution and improves mechanical properties. This study incorporates EST into the conventional cold rolling-quenching-tempering process of M50 steel and investigates the influence and mechanism of applying EST at different stages of the process on the microstructure and mechanical properties. Scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD) were used to characterize the effect of EST on microstructure. The results show that EST can refine the grains of M50 (average reduction of 10.1% in grain size), homogenize the grain size distribution, reduce the dislocation density (20.9% in average), promote the dissolution of carbides in the matrix and distribute them more uniformly along the grain boundaries, resulting in the improvement of mechanical properties. The mechanical properties of the specimen with the process flow of rolling-quenching-tempering-electroshocking showed excellent performance, with an increase in hardness of 1.4%, tensile strength of 17.7%, and elongation at break of 24.3% as compared to the specimen without EST. The tensile properties of the specimen with the process flow of rolling-electroshocking-quenching-tempering showed the best performance, with an increase in tensile strength of 30.0% and elongation at break of 30.7% as compared to the specimen without EST.
The intricate grinding process exposes various cleavage surfaces of mineral particles. This paper systematically investigates the structural characteristics of exposed malachite crystal surfaces and the adsorption behavior and mechanism of hydroxamic acid and water molecules using first-principle density functional theory. The study reveals anisotropic surface energies among crystal surfaces, ranked as
Finding appropriate flotation reagents to separate copper-nickel sulfide ores from various magnesium silicate gangue minerals has always been a challenge in the mineral processing industry. This study introduced xanthan gum (XG) as a non-toxic and environmentally friendly depressant of talc, olivine, and serpentine. The effects and mechanisms of XG on the aggregation and flotation behavior of talc, olivine and serpentine were investigated by flotation tests, sedimentation tests, IC-FBRM particle size analysis tests, adsorption quantity tests, Fourier transform infrared spectroscopy (FTIR) tests, X-ray photoelectron spectroscopy (XPS) analysis tests and Zeta potential tests. The flotation results indicated that when the three minerals were mixed, XG caused the talc-serpentine aggregation in the solution to shift to olivine-serpentine aggregation, with the remaining XG adsorbing on talc to depress its flotation. In addition, combining XPS and zeta potential tests, the —OH (hydroxyl) groups in XG molecules preferentially adsorbed on Mg sites on the surface of olivine through chemical bonding. The surface potential of olivine significantly shifted to a more negative value, with the negative charge on the olivine surface far exceeding that on the talc surface. This resulted in an increased aggregation effect between positively charged serpentine and negatively charged olivine due to enhanced electrostatic forces.
Red mud is a solid waste discharged in the process of alumina production, and how to realize the efficient recovery of its iron is an urgent problem to be solved. In this study, the iron extraction test and mechanism study of high-iron red mud were carried out under the coupling conditions of multiple physical field (microwave field, gas-solid flow field and temperature field) with biomass as the reducing agent. The test results showed that under the optimal conditions, an iron concentrate with a yield of 78.4%, an iron grade of 59.23%, and a recovery rate of 86.65% was obtained. The analyses of XRD, XPS, TEM, and SEM-EDS showed that during the roasting process, the hematite in the high-iron red mud was completely converted to magnetite, and the biomass produced the reductant that provided the magnetization reaction; A large number of cracks and pores appeared in the surface of the hematite reduction product particles, which helped to induce iron minerals to undergo effective mineral phase transformation. The above study provides ideas for the phase transformation and efficient recovery of iron minerals in red mud.
Using solid waste as a substitute for conventional cement has become an important way to reduce carbon emissions. This paper attempted to utilize steel slag (SS) and fly ash (FA) as supplementary cementitious material by utilizing CO2 mineralization curing technology. This study examined the dominant and interactive influences of the residual water/cement ratio, CO2 pressure, curing time, and SS content on the mechanical properties and CO2 uptake rate of CO2 mineralization curing SS-FA-Portland cement ternary paste specimens. Additionally, microstructural development was analyzed. The findings demonstrated that each factor significantly affected compressive strength and CO2 uptake rate, with factor interactions becoming more pronounced at higher SS dosages (>30%), lower residual water/cement ratios (0.1–0.15), and CO2 pressures of 0.1–0.3 MPa. Microscopic examinations revealed that mineralization primarily yielded CaCO3 and silica gel. The residual w/c ratio and SS content significantly influenced the CaCO3 content and crystallinity of the mineralization products. Post-mineralization curing, the percentage of pores larger than 50 nm significantly decreased, the proportion of harmless pores smaller than 20 nm increased, and pore structure improved. This study also found that using CO2 mineralization curing SS-FA-Portland cement solid waste concrete can significantly reduce the negative impact on the environment.
The contact characteristics of the rough tooth surface during the meshing process are significantly affected by the lubrication state. The coupling effect of tooth surface roughness and lubrication on meshing characteristics of planetary gear is studied. An improved three-dimensional (3D) anisotropic tooth surface roughness fractal model is proposed based on the experimental parameters. Considering asperity contact and elastohydrodynamic lubrication (EHL), the contact load and flexibility deformation of the tooth surface are derived, and the deformation compatibility equation of the 3D loaded tooth contact analysis (3D-LTCA) method is improved. The asperity of the tooth surface changes the system from EHL to mixed lubrication and reduces the stiffness of the oil film. Compared with the sun-planet gear, the asperity has a greater effect on the meshing characteristics of the ring-planet gear. Compared with the proposed method, the comprehensive stiffness obtained by the traditional calculation method considering the lubrication effect is smaller, especially for the ring-planet gear. Compared with roughness, speed and viscosity, the meshing characteristics of planetary gears are most sensitive to torque.
This study investigates the shear mechanical responses and debonding failure mechanisms of anchoring systems comprising three anisotropic media and two anisotropic interfaces under controlled boundary conditions of constant normal load (Fs), constant normal stiffness (K), and shear rate (v). A systematic analysis of shear mechanical properties, the evolution of maximum principal strain field, and damage characteristics along shear failure surface is presented. Results from direct shear tests demonstrate that initial shear slip diminishes with increasing Fs and K, attributed to the normal constraint strengthening effect, while an increase in v enhances initial shear slip due to attenuated deformation coordination and stress transfer. As Fs increases from 7.5 to 120 kN, K from 0 to 12 MPa/mm, and v from 0.1 to 2 mm/min, the peak shear load increases by 210.32% and 80.16% with rising Fs and K, respectively, while decreases by 38.57% with increasing v. Correspondingly, the shear modulus exhibits, respectively, a 135.29% and 177.06% increase with rising Fs and K, and a 37.03% decrease with larger v. Initial shear dilation is identified as marking the formation of shear failure surface along anisotropic interfaces, resulting from the combined shear actions at the resin-bolt interface, where resin undergoes shear by bolt surface protrusions, and the resin-rock interface, where mutual shear occurs between resin and rock. With increasing Fs and K and decreasing v, the location of the shear failure surface shifts from the resin-rock interface to the resin-bolt interface, accompanied by a transition in failure mode from tensile rupture of resin to shear off at the resin surface.
The geostress and rock blasting in underground engineering may greatly affect the stress thresholds of surrounding rock. In this study, pre-damage impact tests were first conducted on granite under varying confining pressures (5, 10 and 15 MPa) and numbers of impacts (1, 5, 10 and 15 impacts). Then, uniaxial compression tests were undertaken on the pre-damaged granite to study the evolution of stress thresholds using the crack volume strain method and acoustic emission method. The crack damage stre0sses determined by the two methods were compared. Additionally, based on the rise time amplitude and average frequency, the evolution law of microcracks inside rock specimens was revealed, and an improved acoustic emission method was proposed. The results indicated that as the number of impacts increased, the crack closure stress, crack damage stress, and peak stress of granite specimens initially rose and then declined, while they continuously increased with the confining pressure. The proportion of shear cracks first declined and then rose with greater number of impacts and decreased with higher confining pressure, and that of tensile cracks showed the opposite trend. The improved acoustic emission method was more accurate in identifying the crack damage stress.
The stability of the roof in coal mining is crucial for ensuring safe extraction. Studying the mechanical behavior of rock beams under various conditions is essential for improving coal mining safety. However, research on the dynamic response of rock beams under sudden unloading remains limited. This study utilized a self-developed bidirectional loading and unilateral unloading test system to simulate how sudden lower strata subsidence induces the fracture of upper hard rock beams. Bottom unloading experiments were performed on rock beams with varying thicknesses and spans. The experiments recorded surface crack development and internal damage evolution using high-speed photography and acoustic emission monitoring. The results show that rock beams experience multiple stress reductions after unloading, with the largest reduction occurring in the first stage. Flexural deformation was observed, becoming more pronounced as the thickness-span ratio decreased. Greater thickness increased shear cracks and crack expansion angles, while larger spans promoted tensile cracks, arched crack formation, and notable rock spalling. Acoustic emission analysis showed that signal count and energy increased with thickness and span. Finally, discrete element numerical simulations revealed the critical controlling role of harder rock strata in rock beam failure: when the harder strata are at the top, cracks are sharp, and shear failure is more likely; when they are at the bottom, the overall failure range expands, and cracks tend to form arches. These findings improve the understanding of dynamic rock beam fracture under sudden unloading and offer theoretical guidance for roof stability control in deep mining.
Rock residual strength, as an important input parameter, plays an indispensable role in proposing the reasonable and scientific scheme about stope design, underground tunnel excavation and stability evaluation of deep chambers. Therefore, previous residual strength models of rocks established were reviewed. And corresponding related problems were stated. Subsequently, starting from the effects of bedding and whole life-cycle evolution process, series of triaxial mechanical tests of deep bedded sandstone with five bedding angles were conducted under different confining pressures. Then, six residual strength models considering the effects of bedding and whole life-cycle evolution process were established and evaluated. Finally, a cohesion loss model for determining residual strength of deep bedded sandstone was verified. The results showed that the effects of bedding and whole life-cycle evolution process had both significant influences on the evolution characteristic of residual strength of deep bedded sandstone. Additionally, residual strength parameters: residual cohesion and residual internal friction angle of deep bedded sandstone were not constant, which both significantly changed with increasing bedding angle. Besides, the cohesion loss model was the most suitable for determining and estimating the residual strength of bedded rocks, which could provide more accurate theoretical guidance for the stability control of deep chambers.
In the practical slope engineering, the stability of lower sliding body (region A) with back tensile cracks of the jointed rock slope is received more attentions, but the upper rock mass (region B) may also be unstable. Therefore, in this study, based on the stepped failure mode of bedding jointed rock slopes, considering the influence of the upper rock mass on the lower stepped sliding body, the improved failure model for analyzing the interaction force (FAB) between two regions is constructed, and the safety factors (FS) of two regions and whole region (A and B) are derived. In addition, this paper proposes a method to determine the existence of FAB using their respective acceleration values (aA and aB) when regions A and B are unstable. The influences of key parameters on two regions and the whole region are analyzed. The results show that the variation of the FAB and FS of two regions can be obtained accurately based on the improved failure model. The accuracy of the improved failure model is verified by comparative analysis. The research results can explain the interaction mechanism of two regions and the natural phenomenon of slope failure caused by the development of cracks.
Gypsum rocks are highly susceptible to mechanical deterioration under the coupled effects of wet-dry (W-D) cycles and flow rates, which significantly influence the stability of underground excavations. Despite extensive research on the effects of W-D cycles, the coupling influence of flow rates and W-D cycles on gypsum rocks remains poorly understood. This study investigates the mechanical behavior and deterioration mechanisms of gypsum rocks subjected to varying W-D cycles and flow rate conditions. Axial compression tests, along with nuclear magnetic resonance (NMR) techniques, were employed to analyze the stress – strain response and microstructural changes. Based on the disturbed state concept (DSC) theory, a W-D deterioration model and a DSC-based constitutive model were developed to describe the degradation trends and mechanical responses of gypsum rocks under different conditions. The results demonstrate that key mechanical indices, elastic modulus, cohesion, uniaxial compressive strength (UCS), and internal friction angle, exhibit logarithmic declines with increasing W-D cycles, with higher flow rates accelerating the deterioration process. The theoretical models accurately capture the nonlinear compaction behavior, peak stress, and post-peak response of gypsum specimens. This study provides valuable insights for predicting the mechanical behavior of gypsum rocks and improving the stability assessments of underground structures under complex environmental conditions.
The cemented-gangue – fly-ash backfill (CGFB) prepared from coal-based solid waste materials commonly exhibits high brittleness, leading to an increased susceptibility to cracking. Uniaxial compressive strength (UCS), acoustic emission (AE), and scanning electron microscopy tests were conducted on CGFB samples with recycled steel fiber (RSF) contents of 0, 0.5%, 1.0% and 1.5% to assess the mechanical properties and damage evolution law of the CGFB. The research findings indicate that: 1) When RSF contents were 0.5%, 1%, and 1.5%, respectively, compared to samples without RSF, the UCS decreased by 3.86%, 6.76%, and 15.59%, while toughness increased by 69%, 98%, and 123%; 2) The addition of RSFs reduced the post-peak stress energy activity and increased the fluctuations in the b-value; 3) As the RSF dosage increased from 0 to 1.5%, the per unit dissipated strain energy increased from 5.84 to 21.51, and the post-peak released energy increased from 15.07 to 33.76, indicating that the external energy required for the CGFB sample to fail increased; 4) The hydration products, such as C-S-H gel, ettringite, and micro-particle materials, were embedded in the damaged areas of the RSFs, increasing the frictional force at the interface between the RSF and CGFB matrix. The shape variability of the RSFs caused interlocking between the RSFs and the matrix. Both mechanisms strengthened the bridging effect of the RSFs in the CGFB, thereby improving the damage resistance capability of CGFB. The excellent damage resistance occurred at an RSF content of 0.5%; thus, this content is recommended for engineering applications.
The stability of the “surrounding rock-backfill” composite system is crucial for the safety of mining stopes. This study systematically investigates the effects of steel slag (SS) content and interface angle on the strength and failure characteristics of rock and SS-cemented paste backfill composite specimens (RBCS) through uniaxial compression strength tests (UCS), acoustic emission systems (AE), and 3D digital image correlation monitoring technology (3D-DIC). The intrinsic mechanism by which SS content influences the strength of SS-CPB was revealed through an analysis of its hydration reaction degree and microstructural characteristics under varying SS content. Moreover, a theoretical strength model incorporating different interface angles was developed to explore the impact of interface inclination on failure modes and mechanical strength. The main conclusions are as follows: The incorporation of SS enhances the plastic characteristics of RBCS and reduces its brittleness, with the increase of SS content, the stress–strain curve of RBCS in the “staircase-like” stage becomes smoother; When the interface angle is 45°, the RBCS stress–strain curve exhibits a bimodal feature, and the failure mode changes from Y-shaped fractures to interface and axial splitting; The addition of SS results in a reduction of hydration products such as Ca(OH)2 in the backfill cementing system and an increase in harmful pores, which weakens the bonding performance and strength of RBCS, and the SS content should not exceed 45%; As the interface angle increases, the strength of RBCS decreases, and the critical interface slip angle decreases first and then increases with the increase in the ES/ER ratio. This study provides technical references for the large-scale application of SS in mine backfill.
Utilizing mine solid waste as a partial cement substitute (CS) to develop new cementitious materials is a significant technological innovation that will decrease the expenses associated with filling mining. To realize the resource utilization of magnesium slag (MS) and blast furnace slag (BFS), the effects of different contents of MS and BFS as partial CSs on the deformation and energy characteristics of cemented tailings backfill on different curing ages (3, 7, and 28 d) were discussed. Meanwhile, the destabilization failure energy criterion of the backfill was established from the direction of energy change. The results show that the strength of all backfills increased with increasing curing age, and the strengths of the backfills exceeded 1.342 MPa on day 28. The backfill with 50% BFS+50% cement has the best performance in mechanical properties (the maximum strength can reach 6.129 MPa) and is the best choice among these CS combinations. The trend in peak strain and elastic modulus of the backfill with increasing curing age may vary depending on the CS combination. The energy index at peak stress of the backfill with BFS as a partial CS was significantly higher than that of the backfill under other CS combinations. In contrast, the enhancement of the energy index when MS was used as a partial CS was not as significant as BFS. Sharp changes in the energy consumption ratio after continuous smooth changes can be used as a criterion for destabilization and failure of the backfill. The research results can provide guidance for the application of MS and BFS as partial CSs in mine filling.
During upward horizontal stratified backfill mining, stable backfill is essential for cap and sill pillar recovery. Currently, the primary method for calculating the required strength of backfill is the generalized three-dimensional (3D) vertical stress model, which ignores the effect of mine depth, failing to obtain the vertical stress at different positions along stope length. Therefore, this paper develops and validates an improved 3D model solution through numerical simulation in Rhino-FLAC3D, and examines the stress state and stability of backfill under different conditions. The results show that the improved model can accurately calculate the vertical stress at different mine depths and positions along stope length. The error rates between the results of the improved model and numerical simulation are below 4%, indicating high reliability and applicability. The maximum vertical stress (σzz, max) in backfill is positively correlated with the degree of rock-backfill closure, which is enhanced by mine depth and elastic modulus of backfill, while weakened by stope width and inclination, backfill friction angle, and elastic modulus of rock mass. The σzz, max reaches its peak when the stope length is 150 m, while σzz, max is insensitive to changes in rock-backfill interface parameters. In all cases, the backfill stability can be improved by reducing σzz, max. The results provide theoretical guidance for the backfill strength design and the safe and efficient recovery of ore pillars in deep mining.
The geological structure of coal seams in China is remarkably varied and complex, with coalbed methane reservoirs marked by significant heterogeneity and low permeability, creating substantial technical challenges for efficient extraction. This study systematically investigates the impact of Liquid Nitrogen Immersion (LNI) on the coal’s pore structure and its mechanism of enhancing permeability with a combination of quantitative Nuclear Magnetic Resonance (NMR) analysis, nitrogen adsorption experiments, and fractal dimension calculations. The results demonstrate that LNI can damage the coal’s pore structure and promote fracture expansion through thermal stress induction and moisture phase transformation, thereby enhancing the permeability of coal seams. The T2 peak area in the NMR experiments on coal samples subjected to LNI treatment increases by an average of 15%, the BET specific surface area decreases to 6.02 m2/g, and the BJH total pore volume increases to 14.99 mm3/g. Furthermore, changes in fractal dimensions (D1 rising from 2.804 to 2.837, and D2 falling from 2.757 to 2.594) indicate a notable enhancement in the complexity of the pore structure. With increasing LNI cycles, the adsorption capacity of the coal samples diminishes, suggesting a significant optimization of the pore structure. This optimization is particularly evident in the reconstruction of the micropore structure, which in turn greatly enhances the complexity and connectivity of the sample’s pore network. In summary, the study concludes that LNI technology can effectively improve the permeability of coal seams and the extraction efficiency of coalbed methane by optimizing the micropore structure and enhancing pore connectivity, which offers a potential method for enhancing the permeability of gas-bearing coal seams and facilitating the development and utilization of coalbed methane.
To investigate the effect of rail pad viscoelasticity on vehicle-track-bridge coupled vibration, the fractional Voigt and Maxwell model in parallel (FVMP) was used to characterize the viscoelastic properties of the rail pad based on dynamic performance test results. The FVMP model was then incorporated into the vehicle-track-bridge nonlinear coupled model, and its dynamic response was solved using a cross-iteration algorithm with a relaxation factor. Results indicate that the nonlinear coupled model achieves good convergence when the time step is less than 0.001 s, with the cross-iteration algorithm adjusting the wheel-rail force. In particular, the best convergence is achieved when the relaxation factor is within the range of 0.3–0.5. The FVMP model effectively characterizes the viscoelasticity of rail pads across a temperature range of ±20 °C and a frequency range of 1–1000 Hz. The viscoelasticity of rail pads significantly affects high-frequency vibrations in the coupled system, particularly around 50 Hz, corresponding to the wheel-rail coupled resonance range. Considering rail pad viscoelasticity is essential for accurately predicting track structure vibrations.
The advancement of rail transportation necessitates energy absorption structures that not only ensure safety but also optimize space utilization, a critical yet often overlooked aspect in existing designs. This study presents a compact energy absorption structure (CE) that integrates the advantages of cutting rings and thin-walled tube modules, offering a solution with the high space utilization and the superior crashworthiness. Through theoretical modeling and experimental validation using a drop-weight test system, we analyzed the dynamic response and energy absorption characteristics of the CE. Comparative analysis with existing structures, namely the cutting shear rings (CSR) energy absorption structure and thin-walled tube structure (TW), revealed that the CE significantly improves specific energy absorption (SEA) by 102.76% and 61.54%, respectively, and optimizes crush force efficiency (CFE) by increasing 8.23% and 5.49% compared to CSR and TW. The innovative design of the CE, featuring deformation gradient and delay response strategies, showcases its potential for practical application in engineering, advancing the field of crashworthiness engineering.