Ultrathin 2D niobium oxide dichloride (NbOCl2) is an emerging member of the 2D ferroelectric material family with extensive potential to provide multifunctionality in electronic devices and nanophotonics elements. It exhibits negligible interlayer electronic coupling and significant excitonic behavior in the bulk state. Here we substantiate that NbOCl2 nanosheets can be exfoliated and effectively size-selected using controlled centrifugation techniques by the liquid phase exfoliation (LPE) method. Spectroscopic measurements displayed that the variations in dispersion were highly dependent on the nanosheet dimensions. The nanosheets seemed to be comparatively defect-free which will be further corroborated by high resolution transmission electron microscopy (HRTEM) and Raman analysis. The size selected nanosheets are unanticipated stable in isopropyl alcohol (IPA), possibly owing to the protective influence of a solvation shell. Additionally, the photothermal conversion response and photothermal stability of nanosized NbOCl2 were investigated. Our finding revealed that NbOCl2 possesses a robust photothermal agent property, boasting a photothermal conversion efficiency of more than 30%. This underscores its promising potential for various photothermal applications in different fields such as photothermal therapy and thermal energy conversion.h
The selective reduction of carbon dioxide (CO2) into high-value-added chemicals is one of the most effective means to solve the current energy and environmental problems, which could realize the utilization of CO2 and promote the balance of the carbon cycle. Formate is one of the most economical and practical products of all the electrochemical CO2 reduction products. Among the many metal-based electrocatalysts that can convert CO2 into formate, Sn-based catalysts have received a lot of attention because of their low-cost, non-toxic characteristics and high selectivity for formate. In this article, the most recent development of Sn-based electrocatalysts is comprehensively summarized by giving examples, which are mainly divided into monometallic Sn, alloyed Sn, Sn-based compounds and Sn composite catalysts. Finally, the current performance enhancement strategies and future directions of the field are summarized.
The pure Mg with columnar crystals was prepared by directional solidification, and the effect of process parameters on the crystal orientation and tensile properties was studied. Moreover, the microstructure evolution during tensile deformation was analyzed by electron backscatter diffraction (EBSD) technology. Furthermore, the slip within adjacent grains and grain boundary strain were discussed using the bicrystal model theory. The results show that the microstructure of the pure Mg at a pulling rate of 200 µm/s is columnar polycrystal with growth orientation concentrated in
The influence of grain size or grain refinement on the corrosion of Zr alloy is clarified by employing a series of electrochemical analyses and characterization techniques. The corrosion resistance, as a function of exposure time, F− concentration, and solution temperatures, of Zr alloys with different grain sizes is ascertained. The results confirm that refining the grain size can effectively enhance the short-time corrosion properties of Zr alloy in HNO3 with F−. The fine-grained Zr alloy (∼10 µm in diameter) consistently exhibits a lower corrosion current density, ranging from 18% to 46% lower than that of the coarse-grained Zr alloy (∼44 µm). The enhanced corrosion resistance is attributed to the high-density grain boundaries, which promote oxide stability, and accelerate the creation of the protective layer. The high corrosion rate and pseudo-passivation behavior of Zr alloys in fluorinated nitric acid originate from the accelerated “dissolution-passivation” of the oxide film. However, the grain refinement does not provide enduring anti-corrosion for Zr alloys. To meet the operation of spent fuel reprocessing, additional systematic efforts are required to evaluate the long-term effect of grain refinement.h
Carbonized melamine foam has been recognized as a promising material for microwave absorption due to its exceptional thermal stability, lightweight, and remarkable dielectric properties. In this study, we investigated the impact of nitric acid oxidation on the surface of carbonized melamine foam and its microwave absorption properties. The treated foam exhibits optimal reflection loss of −21.51 dB at 13.20 GHz, with an effective absorption bandwidth of 7.04 GHz. The enhanced absorption properties are primarily attributed to the strengthened dielectric loss, improved impedance matching, and increased polarization losses resulting from the oxidized surfaces. This research demonstrates a promising new approach for research into surface treatments to improve the performances of microwave absorbers.h
In order to obtain high-density dual-scale ceramic particles (8.5 wt.% SiC+1.5 wt.% TiC) reinforced Al-Mg-Sc-Zr composites with uniform microstructure, 50 nm TiC and 7 µm SiC particles were pre-dispersed into 15–53 µm aluminum alloy powders by low-speed ball milling and mechanical mixing technology, respectively. Then, the effects of laser energy density, power and scanning rate on the density of the composites were investigated based on selective laser melting (SLM) technology. The effect of micron-sized SiC and nano-sized TiC particles on solidification structure, mechanical properties and fracture behaviors of the composites was revealed and analyzed in detail. Interfacial reaction and phase variations in the composites with varying reinforced particles were emphatically considered. Results showed that SiC-TiC particles could significantly improve forming quality and density of the SLMed composites, and the optimal relative density was up to 100%. In the process of laser melting, a strong chemical reaction occurs between SiC and aluminum matrix, and micron-scale acicular Al4SiC4 bands were formed in situ. There was no interfacial reaction between TiC particles and aluminum matrix. TiC/Al semi-coherent interface had good bonding strength. Pinning effect of TiC particles in grain boundaries could prevent the equiaxial crystals from growing and transforming into columnar crystals, resulting in grain refinement. The optimal ultimate tensile strength (UTS), yield strength (YS), elongation (EL) and elastic modulus of the SiC-TiC/Al-Mg-Sc-Zr composite were ∼394 MPa, ∼262 MPa, ∼8.2% and ∼86 GPa, respectively. The fracture behavior of the composites included ductile fracture of Al matrix and brittle cleavage fracture of Al4SiC4 phases. A large number of cross-distributed acicular Al4SiC4 bands were the main factors leading to premature failure and fracture of SiC-TiC/Al-Mg-Sc-Zr composites.h
The pronounced anisotropy in mechanical properties presents a major obstacle to the extensive application of aluminum-lithium (Al-Li) alloys, primarily attributed to heterogeneous precipitate distribution, grain structure variations, and crystallographic texture. This study investigates the impact of pre-thermal treatment prior to hot rolling and aging treatment on the anisotropy of mechanical properties of 2195 alloy sheet fabricated by gas atomization, hot pressing and hot rolling. The results demonstrate that pre-treatment at 450 °C for 4 h promotes finer and more uniform distribution of precipitates, effectively mitigating mechanical anisotropy of the alloy sheet. Additionally, this treatment facilitates recrystallization during hot rolling, further reducing mechanical anisotropy. The in-plane anisotropy (IPA) factors for ultimate tensile strength (UTS) and yield strength (YS) are 1.15% and 0.77%, respectively. Subsequent aging treatment enhances grain refinement and the uniformity of the T1 phase, suppresses the formation of precipitation-free zones (PFZs), significantly improving the strength and toughness of the alloy sheet. After peak aging at 165°C for 48 h, the alloy sheet exhibits YS of 547 MPa, UTS of 590 MPa, and elongation (EL) of 7.7%.
In this study, the interaction between deformation and precipitates during multiple equal channel angular pressing (ECAP) deformations and inter-pass aging combination and its effect on the mechanical properties of 7050 aluminum alloy are studied. The result show that ECAP induces numerous substructures and dislocations, effectively promoting the precipitation of the η′ phase exhibiting a bimodal structure during inter-pass aging. Following inter-pass aging and subsequent ECAP, the decrease in grain size (4.8 µm) is together with the increase in dislocation density (1.24×1015 m−2) due to the pinning effect of the precipitated phase. Simultaneously, the dislocation motion causes the second phase particles to become even finer and more diffuse. The synergistic effects of precipitation strengthening, fine grain strengthening, and dislocation strengthening collectively enhance the high strength of aluminum alloys, with ultimate tensile strength and yield strength reaching approximately 610 and 565 MPa, respectively. Meanwhile, ductility remains largely unchanged, primarily due to coordinated grain boundary sliding and the uniform and fine dispersion of second phase particles.h
As cathode materials for alkali-ion batteries, sodium manganese oxides have been receiving considerable and continuous attention in recent decades. In this work, the structure and environment-dependent stability of NaMn2O4 surface were studied based on the first principles calculations. The surface stability diagram of NaMn2O4 involving various different terminations of (100), (110) and (111) surfaces was constructed, and the stability of these different terminations could be compared as a function of chemical environment. It is found that the (100)-MnO and (111)-ONa terminations are two more stable terminations under the investigated chemical conditions. And the surface energies of (110) surfaces are negative under the investigated chemical potential, hence, (110) surfaces are unstable. The surface energy of NaMn2O4 as a function of O chemical potential is also investigated under constant Na chemical potential. The structure relaxation indicates that the surface rumpling and surface reconstruction can affect the electronic structure of the surface, thereby reducing surface energy and stabilizing the surface. Furthermore, the Wulff shape of NaMn2O4 was also constructed based on Gibbs-Wulff theorem.h
In view of the difference in coordination capacity of the glycine ion (Gly−), a selective leaching process for treating with spent lithium-ion batteries (LIBs) in the alkaline glycinate system was proposed. The effects of retention time, leaching temperature, concentration of glycine ligand, liquid-solid ratio (L/S), pH, stirring speed, and H2O2 dosage on the leaching efficiency of valuable metals and the dissolution of impurities were investigated. When the spent LIBs were leached in 3 mol/L glycine aqueous solution with pH of 8, L/S of 5 mL:1 g and H2O2 dosage of 5 vol.% at 90 °C and stirring speed of 400 r/min for 3 h, lithium, cobalt, nickel, and manganese recoveries were 96.31%, 83.18%, 91.56%, and 31.16%, respectively, but Ca, Al, Fe, and Cu were almost insoluble. Meanwhile, the kinetic study showed that the activation energies for the leaching of Li, Co, Ni, and Mn were all in the range of 45–61 kJ/mol. The results indicate that the leaching process is all controlled by chemical reactions.h
Tin phosphide (SnxPy) is an anode for sodium-ion batteries resulting from its exceptionally high theoretical capacity in future. Nevertheless, its application will be hindered by significant volume expansion during charge-discharge cycles and poor electrical conductivity. This study employs a Sn-based metal-organic framework (Sn-MOF) as a precursor for synthesizing tin phosphide nanoparticles. Then Solidago Canadensis L., commonly known as Canadian Goldenrod, is utilized as a biomass carbon carrier to form a composite with tin phosphide nanoparticles. The biomass-derived porous carbon provides additional sodium ion storage sites and serves as a structural scaffold that constrains the volumetric expansion of tin phosphide, thereby enhancing the material’s stability. The fabricated composite exhibits superior electrode electrochemical performance for sodium-ion batteries. It retains a high capacity (489.5 mA·h/g) after 100 cycles at 0.2 A/g. Even after 500 cycles at a high current density of 2 A/g, it still maintains a stable reversible capacity. This study offers a comprehensive exploration of innovative design strategies essential for the development of novel anode materials, paving the way for more sustainable and efficient sodium-ion-based energy storage systems.
Copper is a strategic metal that plays an important role in many industries. In copper metallurgy, electrolytic refining is essential to obtain high-purity copper. However, during the electrolytic refining process, impurities such as arsenic are introduced into the electrolyte, which significantly affect the subsequent production and quality of copper products. This paper first discusses the sources, forms, and transformation pathways of arsenic in copper electrolyte during the electrolytic process, then reviews various arsenic removal technologies in detail, including electrowinning, adsorption, solvent extraction, ion exchange, membrane filtration, and precipitation. Particular emphasis is placed on electrowinning, which is the most widely used and mature among these arsenic removal techniques. The paper evaluates these methods based on arsenic removal efficiency, cost effectiveness, technical maturity, environmental friendliness, and operation simplicity. In addition, the paper explores future trends in copper electrolyte purification, focusing on waste reduction at source, resource utilization, intelligent digitalization, and innovations in materials and processes. This review aims to provide researchers and practitioners with a comprehensive and in-depth reference on arsenic removal methods in copper electrolytes.h
As the proton transport channel and binder within the catalytic layer (CL), the physicochemical properties of the ionomer can affect the CL microstructure and performance of the membrane electrode assembly. In this paper, we select ionomers with different side-chain lengths and investigate the effects of the side-chain structure and content of the ionomers on the performance of membrane electrode assembly (MEA). Electrochemical tests show that at a mass ratio of 10 wt.% of ionomer/Ir (I/Ir), long-side-chain (LSC) ionomer exhibits the best performance (2.141 V@2.00 A/cm2, while short-side-chain (SSC) ionomer is 2.208 V@2.00 A/cm2). The MEA containing LSC ionomer shows better electrochemical performance than the SSC at the same I/Ir mass ratio, especially at high current density. The MEA containing LSC ionomer has a larger average pore size and porosity, which indicates that it may have better mass-transfer properties. From the analysis of voltage loss, it can be seen that LSC ionomers have a smaller ohmic impedance and mass transfer resistance than SSC ionomers. In conclusion, LSC ionomers are more conducive to water-gas transport, which can provide excellent water electrolysis performance. This article focuses on the optimization of ionomer side chains and content, which can enhance PEM water electrolysis performance at lower cost.h
Stemming from the high costs and environmental pollution associated with the use of sodium sulfide in the separation and extraction processes of molybdenum bismuth ore, calcium hypochlorite was introduced as a substitute to facilitate the cleaner production of low-grade molybdenum bismuth ore in this study. The effects of calcium hypochlorite on molybdenite, bismuthinite, and pyrite were investigated through micro-flotation, flotation kinetics, batch flotation, FTIR spectra, Scanning electron microscope energy dispersion spectra (SEM-EDS), and Inductively coupled plasma-optical emission spectra (ICP-OES). The flotation tests results showed that calcium hypochlorite could selectively depress bismuthinite and pyrite. In comparison to sodium sulfide, calcium hypochlorite not only improved the flotation indicators for molybdenum and bismuth concentrates but also reduced the dosage of flotation reagents. Moreover, the chemical oxygen demand (COD) of tailings wastewater significantly decreased when using calcium hypochlorite as a depressant. Mechanism research revealed that the use of calcium hypochlorite as a depressant led to BiOCl precipitation on bismuthinite, which hindered the attachment of the collector. In summary, calcium hypochlorite serves as a more efficient and environmentally friendly depressant compared to sodium sulfide in the industrial production processes of low-grade molybdenum bismuth ore.h
The chemical composition of seawater affects the desulfurization of chalcopyrite in flotation. In this study, desulfurization experiments of chalcopyrite were conducted in both deionized (DI) water and seawater. The results showed that, the copper grade of the concentrate obtained from seawater flotation decreased to 24.30%, compared to 24.60% in DI water. Concurrently, the recovery of chalcopyrite decreased from 51.39% to 38.67%, while the selectivity index (SI) also had a reduction from 2.006 to 1.798. The incorporation of ethylene diamine tetraacetic acid (EDTA), sodium silicate (SS), and sodium hexametaphosphate (SHMP) yielded an enhancement in the SI value, elevating it from 1.798 to 1.897, 2.250 and 2.153, separately. It is particularly noteworthy that an excess of EDTA resulted in a SI value of merely 1.831. The mechanism of action was elucidated through analysis of surface charge measurements, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), extended Derjaguin-Landau-Verwey-Overbeek (E-DLVO) theory, and density functional theory (DFT) calculations.h
The enhancement of chalcopyrite bioleaching with an enriched microbial community by acidified seawater was studied, and the enhancing mechanism was analyzed. The microbial community was enriched at the Dabaoshan mine site, and the treated ore sample had high concentrations of chalcopyrite and galena. The experimental results show that copper extraction from chalcopyrite with an enriched microbial community in seawater was promoted from 13.1% to 62.1% by acidification in comparison with that without acidification. Further analyses of the solutions, solid residues and microbial compositions by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy and 16S rDNA sequencing revealed the promoting effects of acidified seawater. This acidification can increase the biodissolution of chalcopyrite to increase the concentration of iron ions and maintain the redox potential in the range of 360–410 mV. The latter produces an optimal redox environment conducive to chalcopyrite dissolution via Cu2S. The adaptability of the microbial community to a high-salt environment is improved. Chloride ions at 580 mmol/L improve the leaching kinetics of chalcopyrite by increasing the porosity and noncrystallinity of the intermediate elemental sulfur. This study provides a promising way to bioleaching copper minerals using seawater for areas with freshwater shortages.h
Understanding the adsorption behavior of heavy metals and metalloids on clay minerals is essential for remediating heavy metal-contaminated soils. The adsorption of heavy metals and metalloids on illite(001) and sodium-montmorillonite (Na-MMT)(001) surfaces was investigated using first-principles calculations in this study, especially As atom and H3AsO3 molecule. The adsorption energies of the As atom were −1.94 eV on the illite(001) and −0.56 eV on the Na-MMT(001), whereas, the adsorption energies of the H3AsO3 molecule were −1.40 eV on illite(001) and −1.01 eV on Na-MMT(001). The above results indicate that the adsorption was more energetically favorable on illite(001). Additionally, compared to Na-MMT(001), there were more significant interactions between the atoms/molecules on the illite(001). After As atom and H3AsO3 molecule adsorption, the electrons were transferred from mineral surface atoms to the adsorbates on both illite(001) and Na-MMT(001) surfaces. Moreover, the adsorption of As atom on illite(001) and Na-MMT(001) surfaces were more energy favorable compared to Hg, Cd, and Cr atoms. Overall, this work provides new insights into the adsorption behavior of As atoms and As molecules on illite and Na-MMT. The results indicate that illite-rich soils are more prone to contamination by arsenic compared to soils primarily composed of Na-MMT minerals.h
Affected by the geological characteristics of coal bearing strata in western mining areas of China, the double-soft composite roof has low strength and poor integrity, which is prone to induce disasters such as large deformation and roof collapse. Four-point bending tests were conducted on anchored double-layer rock beams with different pre-tightening force and upper/lower rock strength ratios (I/II) based on the digital speckle correlation method (DSCM). The research results indicate that the instability process of anchored roof can be divided into stages of elastic deformation, crack propagation, alternating fracture, and failure collapse. The proportion of crack propagation and alternating fracture processes increased with the increase of pre-tightening force and I/II. The pre-tightening force can suppress the sliding of the upper/lower rock interface, and delay the initiation and propagation of cracks. As I/II increases, the failure mode changes from tensile failure steel strip to shear failure anchor rod. Steel strip can improve the continued bearing effect of anchored roof during crack propagation and alternating fracture processes.h
Determining earth pressure on jacked pipes is essential for ensuring lining safety and calculating jacking force, especially for deep-buried pipes. To better reflect the soil arching effect resulting from the excavation of rectangular jacked pipes and the distribution of the earth pressure on jacked pipes, we present an analytical solution for predicting the vertical earth pressure on deep-buried rectangular pipe jacking tunnels, incorporating the tunnelling-induced ground loss distribution. Our proposed analytical model consists of the upper multi-layer parabolic soil arch and the lower friction arch. The key parameters (i.e., width and height of friction arch B and height of parabolic soil arch H1) are determined according to the existing research, and an analytical solution for Kl is derived based on the distribution characteristics of the principal stress rotation angle. With consideration for the transition effect of the mechanical characteristics of the parabolic arch zone, an analytical solution for soil load transfer is derived. The prediction results of our analytical solution are compared with tests and simulation results to validate the effectiveness of the proposed analytical solution. Finally, the effects of different parameters on the soil pressure are discussed.
Dynamic disturbances certainly reduce shear strength of rock joints, yet the mechanism needs deeper explanation. We investigate the shear behavior of a rough basalt joint by conducting laboratory shear experiments. Constant and superimposed oscillating normal loads are applied at the upper block. Meanwhile, the bottom block moves at a constant shear rate. We investigate the shear behavior by: 1) altering the normal load oscillation frequency with a same shear rate, 2) altering the shear rate with a same normal load oscillation frequency, and 3) altering the normal load oscillation frequency and shear rate simultaneously with a constant ratio. The results show that the oscillating normal load reduces the coefficient of friction (COF). The reduce degree of COF increases with higher shear rate, decreases when increasing normal load oscillation frequency, and keeps constant if the special ratio, v/f (shear rate divided by normal oscillation frequency), is constant. Moreover, we identify a time lag between peak normal load and peak shear load. And the lagging proportion increases with higher shear rate, and decreases with larger static COF. Our results imply that a lower creep rate with a higher normal load oscillation frequency easily destabilizes the creeping fault zones.
Considering the characteristics of deep thick top coal roadway, in which the high ground stress, coal seam with low strength, and a large range of surrounding rock fragmentation, the pressure relief anchor box beam support system with high strength is developed. The high-strength bearing characteristics and coupling yielding support mechanism of this support system are studied by the mechanical tests of composite members and the combined support system. The test results show that under the coupling effect of support members, the peak stress of the box-shaped support beam in the anchor box beam is reduced by 21.9%, and the average deformation is increased by 135.0%. The ultimate bending bearing capacity of the box-shaped support beam is 3.5 times that of traditional channel beam. The effective compressive stress zone applied by the high prestressed cable is expanded by 26.4%. On this basis, the field support comparison test by the anchor channel beam, the anchor I-shaped beam and the anchor box beam are carried out. Compared with those of the previous two, the surrounding rock convergence of the latter is decreased by 41.2% and 22.2%, respectively. The field test verifies the effectiveness of the anchor box beam support system.
The spatial relationship between structural planes and principal stresses significantly affects the mechanical properties of deep hard rock. This paper examines the effect of the loading angle under true triaxial compression. While previous studies focused on the angle HV β between the maximum principal stress and the structural plane, the role of angle ω, between the intermediate principal stress and the structural plane, is often overlooked. Utilizing artificially prefabricated granite specimens with a single non-penetrating structural plane, we set the loading angle β to range from 0ΰ to 90ΰ across seven groups, and assigned ω values of 0ΰ and 90ΰ in two separate groups. The results show that the peak strength is negatively correlated with β up to 45ΰ, beyond which it tends to stabilize. The angle ω exerts a strengthening effect on the peak strength. Deformation mainly occurs post-peak, with the strain values ε1 and ε3 reaching levels 2–3 times higher than those in intact rock. The structural plane significantly influences failure mode when ω=0ΰ, while failure localizes near the σ3 surface of the specimens when ω=90ΰ. The findings enhance data on structural plane rocks under triaxial compression and inform theoretical research, excavation, and support design of rock structures.
Dynamic compression experiments were conducted on red sandstone utilizing a split Hopkinson pressure bar (SHPB) to study the loading rate and high temperatures on their mechanically deformed properties and ultimate failure modes, and to analyze the correlation between the strain rate, temperature, peak strength, and ultimate failure modes. The results show that the mass decreases with the increase of treatment temperature, and the pattern of the stress –strain curves is not impacted by the increase of impact velocity. Under a fixed temperature, the higher the impact velocity, the higher the strain rate and dynamical compression strength, indicating a strain rate hardening effect for red sandstone. With an increasing treatment temperature, the strain rate gradually increases when the impact loading remains unchanged, suggesting a rise in the deformability of red sandstone under high-temperature environment. Raise in both impact velocity and treatment temperature leads to an intensification of the damage features of the red sandstone. Similarly, higher strain rates lead to the intensification of the final damage mode of red sandstone regardless of the change in treatment temperature. Moreover, a dynamic damage constitutive model that considers the impacts of strain rate and temperature is proposed based on experimental results.
Aiming at the problem of deep surrounding rock instability induced by roadway excavation or mining disturbance, the true triaxial loading system was used to conduct graded cyclic maximum principal stress σ1 and intermediate principal stress σ2 tests on sandstone to simulate the effect of mining stress in actual underground engineering. The influences of each principal stress cycle on the mechanical properties, acoustic emission (AE) characteristics, and fracture characteristics of sandstone were analyzed. The damage characteristics of sandstone under true triaxial cyclic loading were studied. Furthermore, the damage constitutive model of rock mass under true triaxial cyclic loading was established based on AE cumulative ringing count. The quantitative investigation was conducted on cumulative-damage changes in circulating sandstone, which elucidated the mechanism of damage deterioration in sandstone subjected to true triaxial cyclic loading. The results show that the influence of the graded cycle σ1 on limit maximum principal strain ε1max and limit minimum principal strain ε3max was significantly greater than that of the limit intermediate principal strain ε2max. Graded cycle σ2 had a greater impact on ε2max and a smaller impact on ε3max. The elasticity modulus of sandstone decreased exponentially with the increased cyclic load amplitude, while the Poisson ratio increased linearly. b of AE showed a trend of increasing, decreasing, slightly fluctuating, and finally decreasing during cycling σ1. b showed a trend of slight fluctuation, large fluctuation, and finally increase during cycling σ2. Sandstone specimens experienced mainly tensile failure, tensile-shear composite failure, and mainly shear failure with increased initial σ2 or σ3. This was determined by analyzing the rise angle-average frequency of the AE parameter, corresponding to the rock specimens from splitting failure to shear failure. Besides, the mechanical damage behavior of sandstone under true triaxial cyclic loading could be well described by the established constitutive model. At the same time, it was found that the sandstone damage variable decreased with increased σ2 during cycling σ1. The damage variable decreased first and then increased with increased σ3 during cycling σ2.h
A high-speed train travelling from the open air into a narrow tunnel will cause the “sonic boom” at tunnel exit. When the maglev train’s speed reaches 600 km/h, the train-tunnel aerodynamic effect is intensified, so a new mitigation method is urgently expected to be explored. This study proposed a novel asymptotic linear method (ALM) for micro-pressure wave (MPW) mitigation to achieve a constant gradient of initial compression waves (ICWs), via a study with various open ratios on hoods. The properties of ICWs and MPWs under various open ratios of hoods were analyzed. The results show that as the open ratio increases, the MPW amplitude at the tunnel exit initially decreases before rising. At the open ratio of 2.28%, the slope of the ICW curve is linearly coincident with a supposed straight line in the ALM, which further reduces the MPW amplitude by 26.9% at 20 m and 20.0% at 50 m from the exit, as compared to the unvented hood. Therefore, the proposed method effectively mitigates MPW and quickly determines the upper limit of alleviation for the MPW amplitude at a fixed train-tunnel operation condition. All achievements provide a new potential measure for the adaptive design of tunnel hoods.