The effects of pretreatment on the precipitation behavior of Al₃Zr precipitates and the recrystallization of spray-deposited Al-Cu-Li alloy were investigated by scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction. It was found that the distribution of Al₃Zr dispersoids in the spray-deposited Al-Cu-Li alloy was heterogeneous. The dispersoid number density is higher in the intragranular and lower near the grain boundaries. The precipitation-free zones are distributed in the intragranular and near the grain boundaries, while a small number of linear clusters are distributed near the grain boundaries. During the homogenization process, the interaction between Zr atoms and dislocation climb caused the precipitation of Al₃Zr dispersoids by fast pipe diffusion. Pretreatment of thermal deformation before homogenization increased the number of dislocations in the matrix, promoted the precipitation of Al₃Zr dispersoids, inhibited local PFZs, improved the particle distribution, and uniformly distributed Al₃Zr dispersoids. After compression by 30% at 673 K, compared with annealing at 573 K for 12 h and compression by 10% at 673 K, the Al₃Zr dispersoids have higher number density, more uniform distribution, and smaller size. After hot compression and solution treatment, the percentages of HAGBs in the three hot compression samples were 30.3%, 21.6%, and 17.3%, respectively.

The effects of equal-channel angular pressing (ECAP) deformation on the microstructure, mechanical properties, precipitation phase distribution and precipitation behaviour of a 7075 aluminium alloy were investigated by scanning electron microscopy, X-ray diffractometry and transmission electron microscopy. The original grain size was refined from 26 µm to 4.5 µm, the tissue distribution was more uniform, and the percentage of high-angle grain boundaries was increased from 8.1% to 48.1%. After ECAP deformation, the deformed grains gradually transformed into sub-crystalline and recrystallised microstructure, the dislocation density was reduced by dynamic recrystallisation, the original rolled β-fibre weave transformed into a C-type shear texture, and the precipitated phase particles gradually broke and refined before being distributed in the matrix. The strength and hardness of the original base material were greatly enhanced by combined second-phase and dislocation strengthening effects, but its plasticity was reduced and a mixed brittle-ductile fracture mode is observed.

In this stuy, a new high-throughput heat treatment method was applied to rapidly optimize the microstructure of metastable β titanium alloy Ti-6.8Mo-3.9Al-2.8Cr-2Nb-1.2V-1Zr-1Sn to obtain high strength and ductility. Continuous temperature gradient solution treatment was created in a tubular furnace at 746–909 ° C (the β-transus temperature (845±5) °Q on a length rod. Then, the gradient soluted sample was cut into four identical ones, three of which were aged for 8 h at 450, 550 and 600 °C, respectively. The effect of solution temperature on age hardening was rapidly achieved, and the gradient microstructure was characterized in detail in one high-throughput sample. The results showed that, the width and spacing of secondary α phase (α_s) decreased with the increase of solution temperature, resulting in the increase of strength and the decrease of elongation, while with the increase of ageing temperature the opposite trend appeared. After solution treatment at 746 °C for 2 h and ageing at 600 °C for 8 h, the hierarchical microstructure composed of the primary α phase (α_p), sub-micro α-rods (α_r), and α_s formed, which contributed superior combination between strength and ductility with the yield strength of 1140 MPa and elongation of 15%, respectively.

In this study, the evolution in microstructure, phase, microhardness and tensile behavior of a Cu-8Al alloy plate during the wire and arc additive manufacture (WAAM) process were investigated. The results reveal that the as-deposited CuAl alloy is composed of coarse dendrites, which gradually transform into relatively fine columnar grains under heat effect, and then the size of the columnar grains increases until becomes stable at the location a few millimeters from the top of the plate. Dendrite segregation of Al exists at the as-deposited region and can be eliminated under heat-effect of the later passes, resulting in homogenization of composition and microstructure. The microhardness at the plate top is about HV160, but decreases sharply to about HV80 when the Al segregation is eliminated and the dendrites transform. In-situ tensile tests reveal that the CuAl plate shows high tensile strength (∼400 MPa) and high elongation (∼50%). Both dislocation slip and grain rotation were observed during the tensile process, and all the specimens showed a dimple fracture mode. Generally, the thin-walled CuAl alloy plate prepared by WAAM is uniform and shows high mechanical property, while a local post heat treatment at relative low temperature is necessary in some conditions.

Low elastic modulus and magnetic susceptibility play a vital role in the design of biomedical alloys. However, many existing bio-alloys do not meet these requirements, which is the main reason for limiting their application areas. Therefore, we present a method that proper Sn addition can lower elastic modulus and magnetic susceptibility in this study. The microstructure, mechanical properties and magnetic susceptibility of Zr-16Nb-xTi-ySn (x=4 wt%, 16 wt%; y=4 wt%, 6 wt%) alloys were studied. With increasing Sn addition, the fractions of β and α″ martensite phases are increasing and decreasing, respectively. Elastic modulus, mechanical strength and elongation are roughly increasing with higher Sn compositions except Zr-16Nb-4Ti-6Sn. The increased Sn concentration from 4 wt% to 6 wt% can reduce magnetic susceptibility, especially in Zr-16Nb-16Ti alloy. These evolutions are closely correlated with the change in microstructural characteristics as phase fractions of β and α″ martensite phases of alloys, which can be ascribed fundamentally to the difference in Sn concentrations. Among these alloys, the Zr-16Nb-4Ti-6Sn alloy shows the best combination of mechanical properties and magnetic susceptibility.

We propose a simple and effective one-step activation route to prepare a hierarchically porous carbon with buckwheat core acting for precursor. The as-obtained porous carbon (BCPC-3) shows high specific surface area (805.91 m²/g) and high pore volume (0.60 cm³/g). As a supercapacitor electrode material for three-electrode, porous carbon delivers an ultrahigh capacitance of 330 F/g (at 0.5 A/g) in 6 mol/L KOH. In particular, it displays a capacitance of 140 F/g even when the current density increases to 100 A/g. In addition, in the two-electrode system, a symmetric supercapacitor based on buckwheat core with a controlled carbon structure can provide an output of 6.1 W·h/kg in a 6 mol/L KOH electrolyte. Therefore, this research offers a straightforward and cost-effective pathway for the fabrication of superior supercapacitor electrode materials.

A practical Zn-MnO₂ battery is still challenged by the deterioration stability under the low current density due to the activeness of water in aqueous electrolyte. Herein, we reported a novel and practical hybrid silica-based ZnSO₄/MnSO₄ mixed solution (Si-ZMSO) electrolyte, which obviously improved the cycle stability of Zn-MnO₂ battery. The Si-ZMSO electrolyte can widen the ESW of electrolyte and restrain the side reaction of zinc anode, which can achieve a good cyclic stability over 400 h for Zn∥Zn symmetrical battery. This novel hybrid electrolyte can also stabilize the cyclic performance of Zn-MnO₂ batteries compared to ZMSO electrolyte. In particular, it exhibits a good capacity retention after 200 cycles under the high cathode loading and low current density. This novel strategy is expected to advance the development of Zn-MnO₂ batteries.

In lithium primary batteries, fluorinated carbon (CF_x) cathode has attracted enormous attention due to its high energy density. However, the CF_x cathode reveals capacity fading sharply at low temperature. In this work, succinonitrile (SN) is used as an electrolyte additive to achieve excellent discharge performance at the temperature range from −20 °C to 60 °C. The obvious enhancement of electrochemical performances is attributed to the participation of succinonitrile in the formation of solid electrolyte interphase, which reduces the electrochemical impedance of battery. It is found that the electrolyte with 10% succinonitrile shows higher discharge platform and specific capacity at low temperature. Compared with the electrolyte without additive, the corresponding discharge capacity is enhanced from 398.8 mA·h/g to 527.3 mA·h/g at 0 °C. This work provides a convenient and lower-viscosity electrolyte system to improve the Li/CF_x primary batteries applications in widen-temperature.

DZ988N, a kind of chelating extractant, was used to separate copper from the sulfuric acid leaching solution of a polymetallic residue containing Co(II), Fe(II), Cu(II) and Zn(II), and its chelating mechanism was investigated. In order to optimize the DZ988N extraction process, the effects of DZ988N concentration (v/v), pH value of aqueous phase, extraction temperature, time and phase volume ratio (O/A) on metal extraction efficiency (η_M) and separation coefficient (β_A/B), were determined in detail. It was found that, under the optimal extraction conditions of DZ988N concentration (v/v) of 25%, pH value of aqueous phase of 2.0, extraction temperature of 25 °C, time of 6 min, and phase volume ratio (O/A) of 1/1.5, the single-stage extraction efficiency of Cu(II) was 97.53%, while Fe(II), Co(II) and Zn(II) were basically remained. In addition, extraction isotherms diagram (McCabe-Thiele diagram) was built to determine that a two-stage counter-current extraction is needed. Under the optimal conditions, the copper extraction efficiency was 99.92% and stripped rate was 99.2%. Finally, 99.63% Cu was enriched into the stripped solution with 7.85 g/L Cu²⁺, and 0.38% was lost.

CaMoO₄ is not only the main component of powellite, but also a key intermediate product in molybdenum metallurgy. The current leaching of CaMoO₄ is mainly in experimental and industrial research, and seldom in theoretical analysis. In this research, lgc - pH diagrams for Ca-Mo-H₂O, Ca-Mo-PO₄-H₂O, Ca-Mo-SiO₄-H₂O, Ca-Mo-CO₃-H₂O, Ca-Mo-Y(EDTA)-H₂O, and Ca-Mo-F-H₂O systems were constructed to predict the dissolution behavior of CaMoO₄ in Na₂EDTA, Na₂SiO₃, Na₃PO₄, Na₂CO₃, and NaF solutions. The diagrams suggest that CaMoO₄ can be dissolved by the five types of solutions and the solid products, for example, Ca₅(PO₄)₃OH, CaSiO₃, Ca₃Si₂O₇, CaCO₃ and CaF₂ were generated depending on the added reagent, while calcium combines with EDTA to form soluble CaY²⁻ in Na₂EDTA solution. The stability regions of CaMoO₄ and solid products are dependent on the ion concentration and pH value. Meanwhile, the proper increase of reagent concentration and pH is beneficial for raising the solubility of molybdenum. The leaching experiments of synthetic CaMoO₄ in various media indicate that CaMoO₄ can be dissolved with a high leaching efficiency which was in accord with the thermodynamic analysis. This work presents the construction of thermodynamic diagrams that is useful in the analysis of the encountered phenomena in molybdenum hydrometallurgy and provides a thermodynamic approach for treating CaMoO₄.

Understanding time-dependency of rock is indispensable for geotechnical applications to estimate long-term deformation and stability of underground structures. This paper introduced a comparison between uniaxial compressive (UC) and Brazilian tensile test (BT) behavior for class I and class II rocks using constant loading rate (CLR) and alternative loading rate (ALR) method, which includes the similarity and otherness of complete stress-strain curves, peak strength, loading rate effect and elastic modulus of two types of test; and time-dependency was also quantitatively analyzed. The results show that the stress—strain curves have a similar law; the correlation coefficient k between UC and BT strength for different rocks is 0.0424–0.1394, and the two strengths can convert to each other; there is a linear relationship between tensile and elastic modulus, with an obvious time-dependency, and the two moduli also can convert to each other; the constant n was taken as index of loading rate dependency for rock, and analyzed the relation to the loading condition, testing environment. The constant n can quantitatively assess the long-term stability of underground structures. A constitutive equation based on n value was proposed to simulate the experimental data for four rocks and the calculated results are fitted very well.

This study experimentally investigated the evolutions of normal stiffness of fractured granites after different temperature treatments. The influences of normal displacement (δ_n), initial aperture (b), temperature (T), and saturated condition on the closing behavior of specimens with different openings under normal stress are systematically investigated. The results show that the changing rate of normal stiffness increases gradually with the increment of normal displacement following a quadratic function. When the normal displacement is the same, the stiffness of the specimen with a larger initial opening is relatively smaller. For specimens with various initial openings, the stiffness of saturated specimens decreases with the increasing T (from 25 °C to 600 °C) by 48.18 % when the rotation angle (α) is 20° and δ_n= 1 mm. When T=25 °C and α=20°, the stiffnesses of dry and saturated specimens are 27.31 GPa/m and 19.32 GPa/m, respectively. Finally, two empirical models are proposed to evaluate the variations in stiffness of specimens which are correlated to the parameters such as T, b, and normal strain, and the predicted results are in good agreement with the experimental results.

In order to study the influence of time effect of boundary drainage on consolidation process, the continuous drainage boundary is introduced to investigate the one-dimensional nonlinear consolidation problem of layered soils. The governing equations for the consolidation problem of layered soils under constant loading are established by introducing the nonlinear relationship between void ratio and effective stress. The analytical solutions of the excess pore water pressure and the average consolidation degrees defined by both settlement and excess pore water pressure of layered soils are derived. The correctness of the proposed solutions is verified by comparing with the finite difference solution and the existing analytical solution. Based on the proposed solution, the one-dimensional nonlinear behavior of layered soils is studied by a detailed parametric study. The results show that, the consolidation behaviors of the layered soils are greatly affected by the interface parameter of drainage boundary, and the consolidation rate increases as the interface parameter increases. Under the condition of continuous drainage boundary, the average consolidation degree defined by settlement increases with the increase of effective stress ratio, but the average consolidation degree defined by excess pore water pressure decreases with the increase of effective stress ratio.

Tortuosity is an important parameter to understand the formation mechanism of water-conducted pathways in deep mine engineering. In this study, a numerical method was proposed to calculate the tortuosity of fractured fault rocks. Convergence tests show that the simulation method has high accuracy. The evolution of tortuosity is consistent with previous studies: it can be divided into four stages, i. e., rearrangement of rock particles, particle migration, continued seepage, and steady water flow. There is an exponential relationship between tortuosity and porosity of fractured rock mass. A new concept (porous tortuosity index) was proposed in this study, which can reflect the spatial distribution of particles and particle size distribution of the fractured rocks and is not affected by the flow behavior of water. In addition, the seepage erosion model considering the tortuosity of the fractured rock mass can improve the calculation accuracy of permeability, non-Darcy coefficient and Forchheimer coefficient, which is fundamental for the prediction of water inrush in weak geological structures.

The aim of this study is to reveal the mechanism underlying the influence of adsorbed water on the deformation of high liquid limit soils, and establish the prediction equation of compressibility coefficient, which is helpful for engineering application. high liquid limit clay, high liquid limit silt and clayey sand were selected for laboratory tests. The initial adsorbed water of the soil samples was controlled by different concentrations of NaCl solution, and the adsorbed water contents of three soil samples in different concentrations of salt solution were determined by thermogravimetric analysis. Meanwhile, the variations of liquid limit (LL) and plastic limit (PL) at different concentrations were also determined by the liquid-plastic limit combine tester. In order to study the effect of adsorbed water on the consolidation characteristics, saturated consolidation tests were carried out on three soil samples under different concentrations of salt solutions. The results show that as the concentration of salt solution increases, the adsorbed water content, LL and PL decrease accordingly. For saturated soil samples with the same initial void ratio, the compression index decreases with an increase in adsorbed water content. At the same modified void ratio, the compression curves of different soils tend to be consistent. Based on the results of this study and those available in the literature, the prediction equations of initial void ratio and compression index were established. Compared with the unmodified void ratio, the modified void ratio can normalize the compression behavior of different soil samples since the adsorbed water plays a skeletal role in the soil. Thus, the precision of the prediction equation of compression index can be improved using the modified void ratio.

Block falling is a rock mass damage disaster that is easily encountered during the excavation of underground caverns. To objectively assess the microseismicity and focal mechanism of block falling of underground intersecting chamber induced by blasting excavation, an array of six uniaxial accelerometers and eight uniaxial geophones were installed around the busbar chamber of underground cavern group of the Baihetan Hydropower Station in China. In the time domain, the seismicity response to production blasting reveals that within 3 h after blasting, microseismicity is in an active phase. In the spatial domain, with the advance of working face, the concentrated stress is distributed around the excavation region, and the damage and deterioration of the rock mass are gradually intensified. The active area of microseismic (MS) events is consistent with the stress concentration region. By analyzing the fracture mechanism based on the moment tensor inversion method, it can be seen that the fracture mechanisms of block falling of the intersecting chamber are dominated by tensile fracture. The research results could provide crucial guiding reference for stability analysis, as well as for rethinking the blasting excavation and support optimization of rock masses in similar large underground cavern.

An experimental study is conducted to investigate the effect of different aggregate types, coarse aggregate content, mass concentration, and cement-sand ratio on the bleeding rate and mechanical properties of cemented paste backfill (CPB). Replacing river sand with unclassified tailing can significantly reduce the bleeding rate. The addition of fine-grained tailing increased the water retention of the mixture by 10%–20% and the 28 d unconfined compressive strength (UCS) by 10%–30%. The sensitivity of the bleeding rate to mass concentration is reduced at 60% coarse aggregate content. Increasing the coarse aggregate content is a way to improve the high-concentration CPB fluidity. There is a coarse aggregate optimal content to maximize the sample strength. Test results show that when the coarse aggregate content is 50%, the maximum CPB strength can reach 6.5 MPa. As the mass concentration increases, the mechanical properties increase proportionally. After curing 28 d, the UCS of the 79% mass concentration sample reached 7.9 MPa. The cement-sand ratio had a greater effect on the mechanical properties, and when the cement-sand ratio increased from 1:6 to 1:4, the UCS at 28 d increased by 54.4%, and the bleeding rate decreased to 1.4%.

The dynamic stress concentration ascribed to the scattering of dynamic disturbances encountered by different structures is an important factor affecting the damage of deep subsurface structures. To study the dynamic response around the underground fluid-filled cavity, a simplified model of the plane P-waves incident in the fluid-filled circular cavity with rock mass structure was established. Series solutions of dynamic stress concentration around the fluid-filled cavity were achieved based on the wave function expansion methods and stress boundary conditions. Using Fourier integral transformation, the expression of dynamic stress concentration factors (DSCFs) around the fluid-filled cavity subjected to transient impact was derived. Then, the relationship between DSCFs and their waveform parameters under steady-state and transient incident waves was quantitatively analyzed. In addition, a numerical model was established using the finite element numerical simulation software LS-DYNA and dynamic stress concentration and failure characteristics around the fluid-filled cavity under transient impact load were simulated. The direction of incident, Poisson ratio, time, and wavenumbers have different effects on the distribution of dynamic stress concentration around the fluid-filled circular cavity.

The tunnel lining structure will withstand diseases such as cracking, collapse and dislocation in earthquake action, and heavy losses will be brought, especially when the tunnel passes through the fault. In this study, FLAC^3D software was used to construct the surrounding rock-lining structure model of the across-fault tunnel based on a tunnel in Sichuan, China. The influence of fault width and dip angle on the dynamic response of tunnel lining structure was studied, and the variation of displacement, internal force and tunnel plastic zone were analyzed. The results showed that the shear effect is the clearest influence of fault fracture zone on the tunnel. The larger the fault dip angle, the more favorable it is to the tunnel lining structure. The larger the fault width, the larger the fault influence zone, and the more unfavorable it to the tunnel lining structure. The results can provide a theoretical basis for the improvement of seismic measures when tunneling through faults.

As a significant lifeblood during earthquake mitigation and post-earthquake reconstruction, railway transportation undertakes crucial tasks. Research on track irregularity induced by earthquakes lays the foundation for driving safety after earthquakes. A total of eighty arbitrary seismic records were chosen, and the distribution mode of seismic residual alignment irregularity was summarized. The differences in vehicle vibration under different distribution modes were analyzed. A target seismic residual track irregularity based on the distribution mode analysis was proposed, and the driving speed threshold after earthquakes was calculated. The research results show that under the action of transverse earthquakes, rails suffer an obvious alignment irregularity, that the amplitude of vertical irregularity is small, and that the distribution mode of alignment irregularity can be divided into unimodal and bimodal irregularities. Both the maximum amplitude of bimodal irregularity and the generated vehicle response are significantly smaller than those corresponding to unimodal irregularity. The latter could be simulated by the product of amplitude of track alignment during earthquakes, attenuation coefficient, shape correction coefficient and sine function. When the peak acceleration of transverse earthquakes is less than 0.25g, there is no need for the vehicle to slow down, whereas when it is larger than 0.25g, the vehicle needs to slow down moderately to meet the comfort requirements.

This paper introduces a moving train model experimental study concerning aerodynamic characteristics of a Fuxing train with a scale ratio of 1:16.8 passing a bridge-tunnel junction under crosswinds. This experiment was carried out using the moving model experimental device independently developed by the Wind Tunnel Laboratory at Central South University. A wireless pressure measuring device mounted on the vehicle body was used to monitor aerodynamic pressure on train surface and the pressure can be used to calculate the aerodynamic force by integration. The results show when the train passes the bridge-tunnel junction under crosswinds, the side force of the train will dramatically change from negative to positive or from positive to negative and the standard deviation of pressure on train windward surface is larger than that on train leeward surface. The aerodynamic change patterns of trains on the windward and leeward tracks are similar, but the side force of the train running on the windward track is generally more significant than that on the leeward track; the main reason is that compared with the train on leeward track, the negative pressure on windward surface is smaller and that on leeward surface is larger.

Suburban metro lines play an important role in daily commuting, which transport passengers from suburban areas to the city center in the morning peak. However, the excessive commuting demand leads to oversaturation on trains and platforms, especially at the stations near the city center. To ease the oversaturation of suburban metro lines, an integrated optimization on inbound passenger control and train service planning including short-turn and non-periodic services has been proposed. The proposed approach aims to reduce the maximum number of stranded passengers at the platforms while the total number of waiting passengers outside stations and the running kilometers of all train services are also minimized. To ensure the feasibility of solutions, the train connections and available rolling stock fleet size have been formulated. A genetic algorithm embedded with brute force is adopted to efficiently solve the proposed large-scale nonlinear model. Finally, a real case of Beijing subway Fangshan line shows that the inbound passenger control and short-turn services help to evidently reduce the stranded passengers at the stations near the city center. Compared with the practical train services without inbound passenger control and the integrated model without short-turn services, the integrated model is able to improve the sum of three objectives by more than 14.8%.

To meet personalized travel demand, ride-sourcing platforms provide differentiated service modes for travelers. These service modes are usually operated independently, and because of the heterogeneity of travel demand, the fragmented ride-sourcing services struggle with imbalances between supply and demand within each sub-market. For that, cross-mode dispatching can be adopted to reduce the vehicle idle time and improve passengers’ experience. However, it may undermine the efficiency of the premium mode, such as increased matching failures. To consider the long-term impact of cross-mode dispatching, the dispatching problem of multi-service modes is modeled by the Markov decision process. A multi-service mode dispatching framework is proposed, comprised of a simulator and a two-stage reinforcement learning algorithm. The simulator provides environment support while avoiding matching failures of premium mode caused by cross-mode dispatching. The two-stage reinforcement learning algorithm refines requests based on the k-nearest neighbor algorithm to solve the problem of the dynamic change of the candidate request set. Experiments show that the framework fulfills 3.1% additional basic requests without the decreasing of fulfilled premium requests, by cross-mode dispatching, demonstrating the feasibility of the cross-mode dispatching and the performance of the framework. Sensitivity analyses are designed to test the robustness of the framework under different scenarios.

Series numerical simulations of fire in the train carriage have been performed by fire dynamics simulator (FDS) in this paper. The main purpose of this study is to investigate the influence of fire source locations and windows breakage on carriage fire spreading. Four locations of ignition source were considered and the trigger temperature of window rupture was set as 400 °C. Parameters, such as temperature, heat release rate (HRR), time of window breakage and flame propagation were monitored. It was found that fire source locations and window breakage affect fire development by changing the fresh air supply of carriage. When the fire occurs in the middle of carriage, heat release rate and combustion intensity are greater than those in ends fire. High temperature will promote windows breakage, and the increasing open area will aggravate the combustion of carriage. The ventilation factor change rate has been introduced to describe the relationship between heat release rate and window rupture. As ventilation is a key factor in the evolution for carriage fires, air circulation between carriage and outside should be avoided as much as possible. Therefore, it is of importance to enhance the fire detection and alarm in the carriage and improve the fire fighting and emergency ability.