Coarse-grained WC-10Co cemented carbides are indispensable for demanding applications such as rock drilling and shield tunneling, yet their development is restricted by poor mixing uniformity and inherent hardnesstoughness trade-off. To address those issues, a series of coarse-grained WC-10Co cemented carbides was developed by systematically tuning the ratios of La₂O₃ and Y₂O₃ additives via co-precipitation and hydrogen reduction. The microstructures and mechanical properties were highly sensitive to this ratio. The optimal balance was achieved at a La: Y mass ratio of 1: 2, yielding a hardness of 86.6HRA, a bending strength of 2201 MPa, and a remarkable fracture toughness of 25.72 MPa·m^1/2. This improvement is mainly attributed to a synergistic interface-pinning mechanism. Specifically, trapezoidal La₂O₃ and spherical Y₂O₃ particles preferentially segregate at the WC/Co phase boundaries, thereby inhibiting abnormal WC grain growth and suppressing the martensitic transformation of ductile face-centered cubic cobalt (Co_FCC). Consequently, optimizing the additive ratio effectively alleviated the hardness-toughness trade-off, providing an effective paradigm for tailoring high-performance cemented carbides through precise powder-mixing engineering.

The effect of cryo-rolling-aging treatments with different sequences on the mechanical properties and electrical conductivity of a highly alloyed Cu-1Cr-0.15Zr alloy for use in metallic molds is investigated. In this regard, X-ray diffraction and transmission electron microscopy are used to characterize the prepared samples under various cryorolled and aged conditions. According to the results of the differential scanning calorimetry analysis and hardness measurement, the optimal aging treatment condition is 120 min at 460 ℃. It is found that among different sequential cryogenic deformation and heat treatments, aging at 460 ℃ and then 90% cryo-rolling lead to the highest ultimate tensile strength (683.2 MPa), while the 90% cryo-rolling and then aging at 460 ℃ result in the highest yield strength (541 MPa) associated with low work hardening capability in CuCrZr alloy. Moreover, the two-stage treatment has the most deformation energy along with appropriate electrical conductivity. According to TEM images and XRD results, depending on the sequences of heat treatment and deformation, the microstructure characteristics vary, i.e., precipitates size and dislocation density varying from 3 to 18 nm and 2×10¹³ to 12×10¹³ m⁻², respectively. It is shown that these microstructural features affect the product's mechanical behavior and electrical conductivity.

To study the evolution of temperature, microstructure, and stress in the intensive quenching process, as well as the mechanism of low probability of cracking in this process, a numerical simulation of the intensive quenching of 40Cr impact specimens is carried out using the simulation software DEFORM. A two-stage intensive quenching process is designed to investigate the effect of different cooling rates of the second half of the process on the surface residual compressive stress. Finally, the numerical simulation is experimentally validated by intensive quenching experiments. The results indicate that the surface layer of the intensive quenching workpiece presents compressive stress, and the core presents tensile stress; the average thickness of the surface layer of compressive stress is 1.5 mm. The cooling of the intensive quenching process presents the characteristics of layer-by-layer, and the microstructure transformation also presents the characteristics of layer-by-layer. This characteristic plays a significant role in compressive stress on the surface. For the two-stage intensive quenching process, the results of simulation indicate that the compressive stress in the surface layer of the workpiece increases with the increase of the cooling rate on the surface in the second half of the process.

With the increasing energy demand and the aggravation of environmental pollution, the rapid synthesis of green and efficient materials has attracted widespread attention. The flash joule heating (FJH) technique employs the Joule effect to rapidly heat materials through high-current-density pulsed currents, achieving temperatures exceeding 3000 K within a few milliseconds. The FJH technique exhibits distinct advantages in the synthesis of various materials, including carbon materials, single-atom materials, high-entropy alloys, and composite materials. This study primarily focuses on the synthesis of functional materials using the FJH technique, including the FJH devices and principles, the development of material synthesis via FJH, the effects of FJH factors, and the application of functional materials in environmental and energy fields. The structure and components can be regulated by the FJH process, and the performance is improved for the applications in hydrogen production, energy storage, and pollutant degradation. FJH represents a promising technique for the rapid synthesis of functional materials. Future research needs to further optimize equipment and process conditions to overcome challenges and promote the practical application of FJH technology.

The rapid growth of the battery industry and the clean energy transition have significantly increased lithium demand. Life cycle assessment (LCA) and techno-economic assessment (TEA) indicate that spodumene processing shows no clear advantage over brine extraction in environmental impact or cost; however, due to its high Li₂O grade and mature technologies, spodumene remains the most economically valuable hard-rock lithium resource and a stable supply source. Flotation is the primary method for spodumene beneficiation. This review summarizes the fundamental properties of spodumene and key flotation factors, including grinding, pretreatment, and pulp characteristics. The (110) and (001) planes dominate flotation behavior, with wet grinding and rod milling favoring (110) surface formation. Alkaline pretreatment enhances flotation by increasing active Al sites. Parameters such as pH, temperature, and dissolved ions significantly affect flotation, although systematic studies remain limited. Progress in flotation reagents, processes, and equipment is reviewed. Current research focuses on selective, low-temperature-resistant, and environmentally friendly collectors, while modifier systems and activator effects (e.g., Mg²⁺, Ca²⁺) are also discussed. Future research should integrate flotation fundamentals with systematic reagent-process-equipment design and sustainability evaluation

Jarosite, a common mineral in acid mine drainage (AMD), influences arsenic mobility, yet its role in arsenite (As(III)) transport remains unclear. This study investigated biogenic jarosite formation and intermediate-phase transformation in an Fe(II)-As(III)-SO₄²⁻ environment using Acidithiobacillus ferrooxidans (Fe(II), 160 mmol/L; As(III), 10 − 200 mg/L). The results show that the bacteria first facilitated the crystallization of an As-rich schwertmannite precursor by oxidizing Fe(II) to Fe(III), and then drove its transformation into jarosite as pH declined. Combined analysis of XRD, FTIR, SEM, and elemental composition showed that Fe(III) and As(III) coprecipitated into biogenic jarosite with substituted arsenic. After 72 h, the highest arsenic fixed efficiency, about 60%, was achieved at initial pH 3.0. XPS results showed that As(III) was the main arsenic species on the surface of the intermediate schwertmannite phase. A threestage mechanism governed the process: microbial Fe(II) oxidation initiated As-rich schwertmannite formation, enabling rapid As(III) sequestration at pH>2.5; declining pH triggered jarosite nucleation on schwertmannite surfaces (transitional phase); and sustained acidity completed transformation to jarosite, partially remobilizing As(III) via schwertmannite dissolution. Regulation of pH and competing anions (e.g., phosphate, nitrate) is essential to optimize sequestration and stability during mineral transformation.

Mixed sulfide-oxide zinc ore (MSOZO) is characterized by a low zinc grade, high oxidation rate, and high slime content; consequently, it is difficult to efficiently recover zinc from MSOZO via a single mineral processing method. To address this, a novel method combining flotation and ammonia leaching is proposed for efficient zinc recovery from MSOZO. Results indicated that 91.87% of the zinc sulfides present in MSOZO were enriched into zinc sulfide concentrates with a zinc grade of 26.11% via froth flotation, while 96.54% of zinc was effectively leached from the flotation tailings using NH₃–(NH₄)₂SO₄. The zinc grade in the ultimate tailings decreased to 0.21%, and the comprehensive zinc recovery rate reached 97.64%. The cyclic leaching results showed that zinc leaching reached dynamic equilibrium after nine cycles, with a zinc concentration of 26.08 g/L and a leaching efficiency of 65.34%. Subsequently, more than 99% of Zn²⁺ in the circulating leachate was converted into ZnS precipitates when using (NH₄)₂S as a precipitant. Mechanistically, zinc in the flotation tailings was mainly leached as stable Zn(NH₃)₄²⁺ complexes, and the leaching process was controlled by internal diffusion with an activation energy of 11.37 kJ/mol. Thus, this study provides an efficient approach for zinc recovery from MSOZO.

To investigate the damage characteristics of sandstone in geotechnical engineering in cold regions under long-term freeze-thaw actions, uniaxial compression tests were conducted on sandstone under different freeze-thaw cycles. During the tests, acoustic emission (AE) monitoring was employed to track changes in AE signals throughout the process, while nuclear magnetic resonance (NMR) was used to analyze pore structure variations in the freeze-thaw sandstone, and a wave velocity tester was applied to measure the wave velocity of sandstone after freeze-thaw damage. The results indicate that as the number of freeze-thaw cycles increases, the peak strength, elastic modulus, and wave velocity of sandstone decrease linearly, while porosity increases linearly. With increasing freeze-thaw cycles, the total energy, elastic energy, and dissipated energy decrease, with the proportion of elastic energy diminishing, making it more prone to transformation into dissipated energy. Sandstone subjected to higher numbers of freeze-thaw cycles exhibits more intense and pronounced AE ring-down counts and AE energy signals, while the correlation dimension gradually decreases. From the perspective of phase space dimension, higher numbers of freeze-thaw cycles lead to reduced convergence of the correlation dimension, and the time series of AE ring-down counts shifts from an ordered sequence to a random sequence, indicating increased disorder in crack development. Based on fractal theory, a damage model linking porosity and strength was established, and a correlated damage model integrating elastic modulus, wave velocity, energy, and strength was further developed. The research findings provide theoretical support for exploring the mechanical behavior of fractured rock masses in cold region engineering.

The temperature rise during drilling operations, caused by frictional heating between the machine and rock, is a critical factor limiting the “depth” and “fidelity” of lunar sampling missions. Experimental studies on the frictional characteristics of machine-rock interaction under lunar-based simulated conditions were conducted, revealing the influence of coring drill bit materials and drilling parameters on the friction coefficient and friction torque under high vacuum and extreme temperature conditions. The results indicate that: (1) the dynamic friction coefficient of machine-rock interaction is influenced limitedly by drilling parameters, with environmental conditions being the dominant controlling factor; (2) the effect of vacuum level on the interfacial friction coefficient is consistent for both diamond and cemented carbide materials, showing a decreasing trend in low and medium vacuum environments, but gradually increasing in high vacuum environments; (3) under extreme temperatures, the dynamic friction coefficient at the diamond–simulated lunar rock interface continuously increases during the heating process, whereas it remains essentially stable at the cemented carbide–simulated lunar rock interface. These findings are expected to guide the optimal design of coring bits and drilling parameters, providing technical and theoretical support for deep, fidelity-preserving coring on the lunar base.

This study introduces an ultrabroadband, low-profile hollow three-dimensional absorbing material (HTDA) with wide-angle performance. The HTDA is fabricated from polylactic acid-carbon fiber and incorporates five resistive frequency-selective surfaces (RFSSs). This design enables dielectric loss through the 3D structure and resonance loss via the RFSSs. To achieve ultrabroadband absorption and enhance oblique incidence performance, the RFSSs and the equivalent dielectric constant of the 3D structure were optimized. Metal patches on the sides further improve the oblique incidence performance. Simulation results show that the HTDA, with a total thickness of 0.134λ_L and periodicity of 0.343λ_L (wavelength at the lowest absorption frequency), achieves a −10 dB absorption band from 6.5 to 40.0 GHz (147.1% fractional bandwidth). The absorber maintains effective performance at oblique incidence angles up to 45° for TE polarization and 70° for TM polarization. Both the simulation and experimental results confirm the effectiveness of the design.

Effective stability management of surrounding rock is critical to ensuring the safety and efficiency of underground coal gasification operations. This study investigates the strain rate sensitivity and damage evolution of coal-measure sandstone under coupled high-temperature and high-strain-rate conditions. Using a custom-built near-uniform high-temperature dynamic loading system, the dynamic mechanical properties, energy dissipation behavior, and fractal features of the rock were examined. Experimental results reveal that at elevated temperatures, coal-measure sandstone exhibits a clear strain rate effect. As the strain rate increases, the dynamic elastic modulus, compressive strength, and energy dissipation density increase by 50.31%, 50.16%, and 495.91%, respectively, while the peak strain decreases by 15.83%. The failure mode shifts from tensile to tensile-shear composite failure, the fractal dimension increases by 17.21%, and the energy dissipation rate declines by 49.82%. A temperature influence coefficient is defined based on energy dissipation density. By integrating this with micro-element strength theory, a damage evolution constitutive model is proposed and verified using MATLAB. This model provides a theoretical basis for evaluating rock stability and developing disaster prevention strategies under high-temperature dynamic loading conditions in similar geological engineering applications.

As shallow resources deplete, mining progresses to greater depths, intensifying high-temperature thermal hazards. Deep high-temperature conditions reduce equipment efficiency, pose significant health and safety risks, and exacerbate surrounding rock instability, increasing mine disaster risks. Heat released from surrounding rock is the main source of thermal hazards in deep mines. To control this, this study proposes tunnel wall insulation as an active cooling solution. A multi-component insulating composite, including straw fibers, SiO₂ aerogel, clay ceramsite, and steel fibers, was developed. Through orthogonal experiments, multi-objective optimization was conducted via range and variance analyses and principal component analysis. Small-scale heat conduction tests validated the thermal performance of various mixtures under high temperatures. Results show that combined adjustment of straw fibers and SiO₂ aerogel enhances insulation, steel fibers improve tensile strength with a minimal thermal impact, and clay ceramsite improves the tensile-compressive ratio. The optimal mix, i.e., 6% SiO₂ aerogel, 3% straw fiber, 10% clay ceramsite, and 0.9% steel fiber, achieves a compressive strength of 43.07 MPa, tensile strength of 5.43 MPa, and thermal conductivity of 0.1998 W/(m·K). This study offers an effective solution for integrated insulation and support materials in tunnels under deep, high-temperature, and high-stress conditions.

To study the mechanical characteristics and energy evolution of rock under cyclic loading, both monotonic loading and multi-stage displacement-controlled cyclic loading test were conducted on fine-grained sandstone under different confining pressures. The results show that the peak strength of the sandstone specimens increases by 103.29% with the rise of the confining pressure under monotonic loading, and the peak strength under cyclic loading is usually improved compared with monotonic loading. Under multi-stage cyclic loading, the elastic modulus, stress, and energy of the sandstone specimens show obvious stepwise evolution characteristics, and their values are positively correlated with the confining pressure. Sandstone specimens under uniaxial conditions show splitting failure with serious fracture, while sandstone under triaxial conditions mainly generates shear failure, and the number of secondary cracks tends to increase with the rise of confining pressure. Compared with monotonic loading, the breakage of sandstone specimens under multistage cyclic loading is more serious. Scanning electron microscopy (SEM) images reveal that fracture surfaces after multi-stage cyclic loading are relatively rough and show typical "shell-like" or "beach-like" morphologies. Furthermore, under higher confining pressure conditions, the proportion of intergranular and intragranular cracks at the fracture surface increases due to the stronger constraint on energy release pathways. The findings can provide some value for the stability assessment of engineered rock mass under cyclic disturbance conditions.

This study systematically investigated cyclic hydraulic fracturing (CHF) under real-time, high-temperature, true triaxial conditions and combined the results with a three-dimensional rough-fracture heat-transfer model. The results show that increasing the maximum cyclic pressure percentage (MCPP) enhances fracture surface roughness, whereas increasing the injection flow rate reduces it. A mathematical response model between CHF parameters and the fractal dimension of fracture surfaces was established. Gray-level co-occurrence matrix (GLCM) analysis indicates that the angular second moment and correlation are significantly nonlinearly negatively correlated with MCPP, while entropy and contrast are positively correlated; the injection flow rate shows the opposite trend. Increasing the MCPP improves the heat transfer efficiency of fracture surfaces, whereas increasing the injection flow rate weakens their heat exchange capacity. The response model between CHF parameters and the overall heat transfer coefficient (OHTC) suggests that a CHF scheme with high cyclic pressure and low injection flow rate is favorable for enhancing heat extraction efficiency in hot dry rock reservoirs. In addition, the OHTC shows an approximately negative exponential relationship with injection velocity and a linear negative correlation with injection temperature, indicating that, within a certain range, higher injection velocity and lower injection temperature promote fracture heat transfer efficiency

The digestion process is one of the most complex stages in industrial alumina production. Precise control of the caustic ratio, as the core parameter governing this process, which is critical for digestion efficiency and product quality, still faces two significant challenges. First, the highly complex mechanism involves multiple coupled chemical reactions, complicating real-time internal state perception. Second, practical implementation is constrained by limited edge computing resources hindering complex algorithm deployment and safety-imposed restrictions on the adjustment range and frequency of control valves, posing significant challenges to the feasibility design of advanced control schemes. To address these issues, a macro-micro synergistic prediction model for caustic ratio in the alumina digestion process is established and a highly feasible edge control strategy is proposed, which takes both deployability and safety into account. Firstly, particle dynamic mechanistic analysis is conducted at the micro-scale, introducing a real-time solidphase aluminum concentration factor to establish an accurate reaction kinetics model of alumina digestion process. Subsequently, a full-process multi-reaction decoupling analysis is performed at the macro-scale, enabling the construction of a macro-micro synergistic full-process prediction model. Furthermore, an easily deployable edge control architecture is established, integrating an actuator-protective model predictive control method to form the industrial edge control scheme. Finally, a semi-physical simulation platform for the alumina digestion process is established for validation. Experimental results demonstrate enhanced modeling and control accuracy while confirming significant industrial feasibility.

Traditional cemented iron tailings backfill (CITB) exhibits poor crack resistance and limited toughness. The incorporation of fibers has been shown to significantly enhance its mechanical performance. However, the rheological behavior, strength characteristics, and damage evolution of fiber-reinforced backfill materials remain insufficiently understood. This study systematically investigates the effects of polypropylene fibers (PPF) on slurry rheology and their subsequent influence on the hardened mechanical properties of CITB. The results indicate that increasing PPF content and fiber length significantly elevates slurry yield stress and plastic viscosity, thereby reducing slurry fluidity, and to some extent, backfill strength, while also influencing damage evolution behavior. Despite these effects, the incorporation of PPF markedly enhances the overall deformation capacity and mechanical performance of CITB. At an optimal fiber content of 0.4 wt.% and a fiber length of 9 mm, the splitting tensile and uniaxial compressive strengths on day 28 increased by 166.67% and 43.01%, respectively. The observed improvement in slurry yield behavior is primarily attributed to the mechanical restraint and interfacial interactions introduced by PPF. Meanwhile, the enhancement in mechanical properties is mainly governed by the fiber-bridging effect, which effectively suppresses crack propagation and significantly reduces the rate of damage accumulation. Based on the experimental results, a damage constitutive model incorporating fiber reinforcement effects was developed, demonstrating good agreement with the observed stress− strain behavior of CITB. These results provide valuable theoretical and practical guidance for optimizing fiber-reinforced backfill design and improving the mine backfill operations’ safety and stability.

Empirically based seismic analysis methods that rely on recorded ground motions are routinely used to evaluate structural damage and guide the design of high-speed railway track-bridge systems (HSRTBS). Their accuracy, however, is constrained by the sparse distribution of seismic stations, especially in rugged terrain where ground-motion variability is pronounced. To overcome this limitation, this study utilizes high-precision, physics-based numerical simulations to model complex spatial seismic wavefields. Leveraging the sub‑fault input interface provided by SPECFEM3D, we construct a kinematic hybrid source model of the 2016 Meinong M_w 6.4 earthquake and simulate the complete source-path-site process. The resulting wave field is validated against observed records and by comparing RotD50 intensity measures with the NGA‑West2 ground‑motion prediction equations. After verification, a detailed dynamic analysis of the HSRTBS is performed under both the synthetic and recorded seismic excitations. The results show excellent agreement, demonstrating that physics-based ground-motion simulations can effectively characterize the spatiotemporal evolution of seismic wavefields in complex terrain. This method addresses the limitations of sparse seismic station records and provides reliable, site-specific, and spatially variable seismic inputs. These findings confirm the feasibility and robustness of physics‑based ground‑motion simulations as a reliable alternative to conventional empirical approaches for the seismic analysis of the HSRTBS.

Natural discontinuities, such as holes and cracks in rock masses, often act as stress concentration zones, rendering them highly susceptible to spalling failure under dynamic loading conditions, a critical threat to the safety and stability of underground structures. Filling reinforcement is an effective means to control this kind of damage. Therefore, in this study, the effects of filling material strength and filling radius on the dynamic mechanical response and spalling failure characteristics of holed sandstone are systematically studied using a φ 50 mm split Hopkinson pressure bar (SHPB) system and PFC2D numerical simulation method. The results demonstrate that increasing both the strength and radius of the filling material significantly enhances spalling resistance, delays crack initiation, and reduces the number of spalling cracks, underscoring its capacity to buffer stress waves and modulate fracture development. High-speed imaging directly captures the delayed initiation and propagation of cracks within the filling material. The numerical simulation results further reveal that the filling position is another key factor affecting the reinforcement effect. Fillings at the transmission end experience greater stress superposition, resulting in more severe spalling damage compared to those at the input end. These insights offer practical guidance for optimizing filling strategies in practical engineering applications.

Aiming at the problem that the deterioration mechanism of concrete in a composite salt environment is unclear and the service life is difficult to predict accurately, this study systematically investigated the deterioration law and life prediction under the combined erosion of bicarbonate, sulfate, and chloride. Through the mechanical and dynamic index test of 1–13 months of age, the comprehensive damage index is constructed, and the Weibull model is used to describe its evolution law. Based on the non-parametric Monte Carlo resampling method of experimental data, the confidence interval and reliability estimation of damage degree are realized, and the uncertainty of life prediction is quantitatively characterized. Combined with multi-scale microscopic tests such as XRD and X-CT, the deterioration mechanism of concrete from early densification to crystal growth and decalcification under the action of composite salt was clarified, and the quantitative correlation between pore parameters and macroscopic damage was established. The multiple coupling of mechanism analysis, life prediction, and reliability evaluation was realized, which provided a new theoretical basis and methodological support for the durability prediction of concrete in a complex service environment.

Damage analysis and control based on post-seismic running performance is a research frontier direction of the high-speed railway track-bridge system (HSRTBS), but the relationship between damage features and post-seismic running performance is not clear at present. Therefore, this study employs data-driven methods to obtain interpretable correlation models linking various damage features to post-seismic running performance, which differ from the analytical mapping models used in previous studies and offer greater applicability. The performance of the correlation model is evaluated to determine the recommended regression method, and a sensitivity analysis is conducted to discuss the range of consideration and the key factors governing damage features. The results show that the post-seismic running performance quantified by the derivative of rail deformation (DRD) is mainly related to the damage characteristics within the corresponding beam end position range, and is more susceptible to the influence of fastener and beam end damage characteristics. Based on the existing research on DRD limits and the correlation models proposed in this paper, the damage limits of key components related to post-seismic running performance can be further determined, providing a valuable reference for the damage evaluation and control of the HSRTBS based on the post-seismic running performance.

To study the spanwise correlation characteristics of buffeting forces of the train under the stationary thunderstorm downburst wind, a thunderstorm downburst wind test device was used to simulate the thunderstorm downburst wind fields over two types of surface roughness. Based on rigid model pressure measurement test, the radial wind profiles of the stationary thunderstorm downburst wind and the surface pressures of the train at different radial distances were obtained. The study investigated the effects of radial distance on the train's aerodynamic force coefficients and surface pressure coefficients. Based on this, it analyzed the influence of radial distance and spanwise spacing on the spanwise correlation of buffeting forces in the time domain. Additionally, a comparative analysis was conducted between the spanwise correlation of buffeting forces and the spanwise correlation of fluctuating wind. The research results show that compared with atmospheric boundary layer wind fields, the distribution of the thunderstorm downburst wind fields exhibits significant non-uniformity in the spanwise distribution. Under the thunderstorm downburst wind, the total aerodynamic coefficients and radial wind speed of the train vary with radial distance. When the radial distance r/D_j = 1.0, the radial wind speed reaches its maximum value. As surface roughness increases, the lift coefficient and the RMS value of fluctuating wind pressure coefficient at the junction between the top and the windward side increase, while the lateral force coefficient and radial wind speed decrease overall. Simultaneously, radial wind speed decays more significantly in the outer region (r/D_j > 1.0), radial distance significantly influences the correlation coefficient of buffeting forces. Additionally, the correlation coefficient of buffeting forces gradually decreases with increasing spanwise spacing, indicating a weakening spatial correlation. The correlation for lateral force is superior to that for longitudinal and vertical fluctuating wind, while the correlation of moment is relatively weaker.

Based on the typical meteorological characteristics of a railway in western China, the three-dimensional compressible SST k-ω turbulence model and overset mesh technology were adopted to investigate the pressure characteristics of a full-scale eight-carriage train passing through a single-track tunnel. The rationality of the simulation method was verified through comparison with experimental results from the reference. A method combining the improved Hilbert-Huang transform (HHT) with proper orthogonal decomposition (POD) was proposed to study the pressure field structures at the head and tail trains. Finally, the sliding window-based permutation entropy (SWPE) was introduced to quantify the degree of disorder of the flow field. The results indicate that when a train is traveling through a tunnel, for the head train, the pressure wave dominates the primary mode and stimulates a strong response in the bogie; for the tail train, it couples with and amplifies the serpentine motion of the airflow around the bogie. From a dynamic perspective, the pressure waves promote the flow transformation into a more ordered and low-entropy state.

Existing models for predicting the resilient modulus of subgrade soils can accurately characterize the dynamic stress zone. However, they suffer from two primary limitations: 1) an inability to predict modulus values within the nodynamic stress zone, and 2) the inaccessibility of these modulus values through conventional dynamic triaxial tests. To address these shortcomings, this paper introduces a comprehensive methodology for determining the resilient modulus of subgrade soil under a wide range of stress states. The no-dynamic stress zone is conceptualized as comprising two distinct zones: the no-stress zone and the self-weight stress zone. First, an integrated testing framework encompassing the entire subgrade domain is proposed. For the dynamic action zone, a testing method accounting for the combined influence of dynamic and static stresses is employed. For the area devoid of dynamic action, a novel testing method based on the dynamic triaxial apparatus is presented to measure the soil modulus in the no-dynamic stress zone. This method determines the modulus by maintaining constant confining and contact stresses while progressively reducing the cyclic stress. Subsequently, utilizing Gene Expression Programming (GEP), a unified prediction model integrating both the traditional resilient modulus and the modulus under no-dynamic conditions is developed, incorporating four fitting parameters. When the cyclic stress is below 10 kPa, the dynamic resilient modulus of the subgrade soil increases with increasing cyclic stress; when the cyclic stress exceeds 10 kPa, the modulus decreases with increasing cyclic stress. In contrast, under relatively high cyclic stresses, the dynamic resilient modulus decreases as the cyclic stress increases. Compared to the classical NCHRP 1-28A, Uzan, Ni, and K-θ models, the prediction error under small cyclic stresses is reduced from 15.49%, 16.15%, 18.85%, and 22.77%, respectively, to 4.68% using the proposed model. Furthermore, the model maintains high prediction accuracy across a total of 144 working conditions tested on 7 soil samples.

This study evaluates the seismic performance of high-speed railway continuous girder bridges with concretefilled steel tube piers (CFST) and the corresponding running safety of trains. A refined three-dimensional finite element model considering ductile damage of steel, plastic-damage evolution of confined concrete, and a main-crack insertion technique was developed and validated against shake-table test results. Based on this model, a coupled train-CRTS III slab ballastless track-continuous girder bridge model was established to perform nonlinear time-history analyses under six peak ground acceleration levels from 0.07g to 0.38g and train speeds of 150, 250, and 350 km/h. The results indicate that the predicted wheel-rail forces, vehicle accelerations, and rail/slab displacements under the benchmark service condition are all below code limits and within or close to published field ranges. Under seismic excitation, pier-base plastic damage increases progressively with ground-motion intensity, whereas stirrup-confined concrete-filled steel tube piers (SCFST) show delayed damage initiation and lower damage severity than conventional CFST piers. Both seismic intensity and train speed increase the derailment coefficient and wheel-rail lateral force, while the wheel-load reduction rate is influenced mainly by train speed. The maximum safe train speed for SCFST bridges is 350 km/h at 0.15g and 150 km/h at 0.20g, and train operation should be suspended when the peak ground acceleration reaches 0.25g. Stirrup confinement, therefore, improves both the seismic resistance of CFST piers and the running safety margin of high-speed trains.

Switch panels in railway turnouts are critical for route transitions, but their complex nonlinear behavior complicates vibration analysis. This study integrates hammer testing with an explicit LS-DYNA finite element model to compute frequency response functions and systematically assess sensitivity to modeling parameters (mesh, excitation points, hourglass control and damping). Results show that including nonlinear baseplate contact is essential for capturing the dynamic response in the 300 – 1000 Hz range; without it, simulated resonance peaks shift and attenuate. A fundamental frequency bifurcation around 50 Hz is observed, triggered by coupling between locking devices and railhead contact beyond baseplate 12.5. This interaction intensifies nonlinear effects above 500 Hz. Additionally, iron blocks suppress vibrations below 500 Hz, while fillers limit vibration transmission to one sleeper span and reduce high-frequency peaks above 1500 Hz. Operating deflection shape analysis reveals dominant resonant wavelengths and baseplate deformation modes, with significant deviations from linear behavior above 567.6 Hz due to contact nonlinearities. This explicit finite element approach effectively simulates impact dynamics, providing valuable insights for fatigue prediction and turnout design optimization.