In order to solve landslides and slow infiltration rate in in-situ leaching process of weathered crust elution-deposited rare earth ore (WCE-DREO), the swelling inhibition performance and mechanism of polyethyleneimine (PEI) on montmorillonite (MMT) and WCE-DREO were investigated. The swelling inhibition effect on MMT and WCE-DREO increased gradually with increasing concentration of PEI. The leaching efficiency of rare earths was increased from 93.94% to 95.24% by the compound leaching agent consisting of 0.4% PEI and 2% ammonium sulfate compared to 2% ammonium sulfate alone, and the leaching time was reduced by about 33%. PEI can produce a large amount of —NH₃⁺ by hydrolysis, which can neutralize the negative charge on the interlamination and surfaces of clay minerals, reduce the electrostatic repulsion, and weaken the hydration and swelling of clay minerals. A polymeric film was formed on the clay particles by PEI coating, which changed the hydrophilicity of the particle surface, reduced water intrusion. Small particles were agglomerated by the wrapping and linking effects of long-chain PEI, thus increasing the particle size and facilitating the percolation of leaching agent. PEI skeleton also could embed in the clay interlayer and extrude the interlayer water, which inhibits the swelling of clay minerals.

To improve the hot corrosion performance of TiAl alloys, an Al-Y coating was prepared by a pack cementation process. The effect of catalysts on the structure of the Al-Y coating and its thermal shock resistance was studied. The thermal corrosion performance of both the TiAl alloy and the coating in a mixed molten salt system of 25% NaCl+75% Na₂SO₄ (wt.%) was comparatively investigated. The results showed that the Al-Y coatings prepared with different catalysts had similar structures and good metallurgical bonding with the substrate, which was mainly composed of an Al-rich outer layer, a TiAl₃ middle layer, and a TiAl₂ inner layer. However, the coating prepared using NH₄Cl as the catalyst was more uniform and denser than those formed using NaF and AlCl₃·6H₂O. The Al-Y coating improved the thermal shock resistance of the TiAl alloy under thermal shock at 1273 K. Hot corrosion tests showed that the lamellar α₂-Ti₃Al phase in the TiAl alloy first underwent selective corrosion by O and S atoms in the medium, followed by catastrophic corrosion. Moreover, the Al-Y coating formed a dense Al₂O₃ film in the early stage of hot corrosion, which effectively protected the permeable layer. Upon extending the hot corrosion time, the coating gradually cracks due to the internal and external diffusion of atoms and corrosion stress. The formed cracks served as diffusion channels for S and O atoms, and the TiAl₃ phase in the coating continued to decompose, providing more Al atoms to the cracks. This eventually formed a dense layer of Al₂O₃ to compensate for the cracks, delaying the internal diffusion rate of S and O atoms, and significantly improving the thermal corrosion resistance of the TiAl alloy.

The hot compression tests of Al-5.6Zn-2Mg aluminum alloy were conducted on a universal testing machine at temperature of 300–500 °C and strain rate of 0.1–0.0001 s⁻¹. The work hardening rate curves for the σ_c and ε_c for the onset of dynamic recrystallization were identified. The correlation among the key features σ_c (ε_c), σ_p (ε_p) and σ_SS, and the Z coefficient are determined. Four constitutive models include the Arrhenius-type model, modified Johnson Cook (MJC), modified Zerilli-Armstrong (MZA), and an artificial neural network (ANN) developed. The results showed that the ANN and Arrhenius-type models had the lowest AARE values of 0.486% and 3.36%, while the MZA and MJC models had higher AARE values of 8.84% and 3.93%, respectively. The Arrhenius-type model was found to be the most appropriate prediction model due to its ability to handle the nonlinear relationship among factors, but the MJC model could be a simpler alternative in cases where material properties are unknown or experimental data are limited. The MZA model was found to be unsuitable for estimating flow stress in hot compression. In addition, the highest predictive performance is seen in the best-trained ANN model, with an AARE of 0.486% and an R value of 0.99.

Mg/Al composite plate combines the light weight of Mg alloy and the plasticity and corrosion resistance of Al alloy, which significantly enhances its comprehensive performance. However, the long manufacturing cycle and high process requirements limit the rapid development of heterogeneous composite plate forming technology. Therefore, a new method of ARB (accumulative roll bonding) forming with hard plates is proposed in this paper. The results show that the tensile strength of Mg/Al composite plate can reach 235 MPa and the elongation is 14.7% at 3ARB. There are obvious dimples in the magnesium plate, which are ductile fracture characteristics, and the overall performance is the highest. Since the basal slip and non-basal slip of the Mg plate start at the same time, which promotes the formation of dynamic recrystallization. At this time, the recrystallization ratio of the Mg plate is 77.21%. With the progress of ARB, the high angle grain boundary increases and the grain refinement is obvious. The original grains have been basically broken and refined into equiaxed grains. The hardness fluctuation of Mg and Al matrix decreases gradually, and the internal structure of the composite plate tends to be stable. This provides a new idea for forming and manufacturing high-performance heterogeneous composite plates.

A multilayered composite structure with ultra-wideband and strong microwave absorbing performance has been developed, which is prepared through vacuum bag molding process, and the fiberglass enforced epoxy laminate (FEPL) array on its surface is fabricated by computer numerical control (CNC) carving method. The surface density of the whole composite structure with FEPL array is about 2.4 kg/m², and the thickness is about 10.0 mm. Both simulation and measurement results confirm that FEPL array can considerably improve stability of the incidence angle, increase absorptivity, and broaden the absorption bandwidth. The FEPL array enhances the oblique incidence performance of the composite structure ranging from 40° to 60°, while simultaneously expanding the fractional bandwidth (FBW) by approximately 9.1%. Moreover, it achieves a notable reduction in the average reflection coefficient at normal incidence, decreasing it by about 11.3 dB from −14.4 dB to − 25.7 dB. High performance and simple preparation processes for composite structure indicate that it is suitable for practical engineering applications.

In this study, the Gleeble tests and hot stamping of practical part of Zn-coated hot stamping steel were conducted. Based on the analysis of thermal properties, a material model was employed to fit the relationship between true stress and true strain with high accuracy. The effect of forming temperature, ferrite formation and bending on the liquid metal induce embrittlement (LMIE) was researched. The results show that the true stress increases as forming temperature decreases. LMIE occurs, leading to a low true strain of about 0.13, as the forming temperature reaches 820 °C. According to the Gleeble simulation test and the actual test results, the forming temperature is suggested to be 720 °C. So, LMIE is avoided and the mechanical properties are guaranteed. In practical application, the tensile stress is easy to produce microcrack while the compressive stress constrains it. With the decrease of stamping temperature, the number and width of the microcrack in the coating layer decrease, and the thickness of the coating layer increases. The coating layer is composed of solid α-Fe(Zn) phase. Decreasing the liquid phase in heating, soaking and forming period tends to reduce and even avoid the LMIE cracks.

Nacre-inspired TiB₂/Al-Cu composites were prepared by freeze casting and squeeze casting. This study focused on the effect of gelatin content on microstructure, mechanical characteristics, and wear resistance of the composites. The structure formation, as well as the fracture and wear mechanisms of the composites, was analyzed. The results demonstrate that both the compressive and bending strength and the toughness of the TiB₂/Al-Cu composites improved with gelatin addition. The composites with 1.0 wt% gelatin content achieved optimal mechanical properties, with a compressive strength, bending strength, crack-initiation toughness (K_IC), and crack-growth toughness (K_JC) of (625±13) MPa, (626±4) MPa, (22.23±0.2) MPa ∙ m^1/2, and (54.43±2.4) MPa ∙ m^1/2, respectively. Moreover, the gelatin addition improved the wear properties of the laminated TiB_2/Al-Cu composites significantly. The bent ceramic layer and increased ceramic bridging are responsible for the improved strength, toughness, and wear resistance of the TiB₂/Al-Cu composites inspired by nacre with gelatin addition, which further increased the potential of multiple cracks and reduced the Al layer’s ability to deform plastically.

High-energy-density lithium-sulfur (Li-S) batteries are among the most promising energy storage devices, but their potential has been constrained by the shuttle effect and poor active material utilization. Here, 3,3′-dithiodipropionic acid (DTPA), an efficient electrolyte additive, is applied to Li-S batteries while its underlying mechanism on the electrochemical performance is examined. The results show that the DTPA additive can quickly interact with the polysulfides scattered in the electrolyte, facilitating the conversion of long-chain polysulfides to Li₂S₂ and Li₂S. In this way, by lessening the shuttle effect of long-chain polysulfides towards the anode, the redox kinetics and the usage of active materials can both be improved. The electrochemical performance of Li-S batteries is thus enhanced by the addition of DTPA, with capacities of 1093.4 mA · h/g for the initial cycle and 714.8 mA · h/g after 250 cycles at 0.5C (DTPA concentration is 1.5 wt.%). Also, the DTPA-containing batteries have higher electrochemical stability, with a capacity retention rate of 57.5% relative to 0.1 C at 2C. The improved performance demonstrates the importance of electrolyte additives, and the DTPA introduced in this work offers a potential solution for reducing the shuttle effect of polysulfide to increase the capacity of Li-S batteries.

Deep treatment, a method for further reducing the content of a target substance, for toxic arsenic (As) from water is vital to reduce environmental pollution and ensure human health. Here, we employed electrosorption of As(V) from water in a self-made three-dimensional reactor with granular activated carbon (GAC). The As(V) concentration can be decreased from 0.5 to 0.032 mg/L under optimal conditions, and all of the As practically presented as H₂AsO₄⁻ without As(III), indicating that there was no redox reaction. After kinetic studies and comparisons of pseudo-second-order kinetic, intra-particle diffusion and Boyd models, the electrosorption could be divided into three steps: internal diffusion from the surface of materials to internal pores, liquid film diffusion from the solution to the surface of materials, and the closure of the entire adsorption process to the equilibrium state. In order to verify the cyclic performance of this process, electrosorption-electrodesorption process research was carried out, and it was found that after 8 cycles, the concentration in the effluent was still only 0.098 mg/L, which was lower than the limitation. Above all, both removal efficiency and disposal of adsorption materials should be ameliorated even though As(V) could be removed in depth and recycled.

Humification is one of the critical processes in the ecological restoration of bauxite residue deposit areas. Straw addition is widely used strategy to increase organic carbon in bauxite residue. However, the effect of straw application on the humic carbon fractions in bauxite residue is largely unknown. In this study, the accumulation of humic fractions and associated microbial communities in bauxite residue following straw application were evaluated by humus fractionation and high-throughput sequencing technology. The results showed that straw application significantly increased humic carbon fractions (humic acid and fulvic acid) and humification degree in bauxite residue. The content of humic acid and fulvic acid increased by 27.1% and 22.9% in straw-amended bauxite residue after phosphogypsum addition, respectively. The glucosidase, cellulolytic enzyme, polyphenol oxidase and peroxidase increased by 7.15–8.76 times, 5.64–7.12 times, 2.69–4.57 times and 2.59–4.24 times following the straw application. High-throughput sequencing results indicated that the operational taxonomic unit (OTU) numbers and Shannon index of both bacterial and fungal communities significantly increased following co-application of straw and phosphogypsum. In addition, co-application of straw and phosphogypsum significantly increased the relative abundance of Devosiaceae, Rhizobiaceae, Flavobacteriaceae, Caulobacteraceae, and Cellvibrionaceae in bauxite residue. These findings provide us with a biological perspective of straw on the humification process in bauxite residue.

The compressive properties of coal under water-gas coupling were studied based on the water-rock-gas coupling test system. The compressive strength and deformation damage characteristics of the coal samples were analyzed, and the macro and fine degradation mechanisms of coal under water-gas coupling were revealed. The compressive strength of the coal samples under the three soaking conditions was reduced compared to that of the dry coal samples. The damage mode of coal samples changed from tensile damage of dry coal samples to mixed shear-tensile damage. Coal samples changed from brittle damage to plastic damage, which increased the range of localization zones and the misalignment of coal samples after soaking. The deterioration effects of coal samples in the three soaking environments were mainly as follows: 1) The intrusion of water and gas led to the decomposition and precipitation of clay minerals inside coal samples; 2) The surface of each group of coal samples showed a deterioration effect after soaking; 3) The deterioration effect of water and gas changed the internal pore structure of coal samples. The destruction of the original supporting structure of the coal samples in the soaked environment reduced the ability of the coal samples to store energy before destruction.

Defects in rock masses have significant influence on the fracture propagation during blasting. In this study, a numerical model is developed using the local cohesive element based on the global finite element method (LCEM-GFEM) to simulate the damage evolution and fracturing pattern of rock mass with defects under blasting load. The influence of defect morphology on the stress wave transmission and attenuation is quantified by introducing the energy transfer coefficient. The numerical results show that the defect morphology has prominent influence on the damage characteristics and fracture propagation of rock masses. The merging path of the blast-induced fracture and the derivative fracture shifts from the end to the middle of the defect as the angle of parallel defects increases. The energy transfer coefficient increases with the angle of parallel defects, while the fractal dimension decreases in this case. The number of fractures between the parallel defects and the energy transfer coefficient reduces significantly with the horizontal distance between parallel defects. With the increase of perpendicular distance between the vertical defects, the length of the main horizontal fracture passing through the defect C increases, as well as the energy transfer coefficient and fractal dimension. The numerical results would be beneficial to the understanding of the damage characteristics of defective rock masses under blasting load.

Misalignment and spalling of bearing rings are typical errors and faults that significantly influence the vibration characteristics of a gear-rotor-bearing system. In order to investigate the coupling effects of misalignment and spalling, it is necessary to analyze the vibration characteristics of a gear-rotor-bearing system with misalignment and spalling. Firstly, considering the outer ring misalignment and spalling, the 5-DOF nonlinear bearing restoring force is calculated. Then, based on the loaded tooth contact analysis (LTCA) method, the meshing stiffness is calculated, and the dynamic model of the spur gear pair is established. Furthermore, the equivalent stiffness model of the spline is established based on the slicing method. Finally, by coupling the bearing restoring force model, the dynamic model of the spur gear pair, and the equivalent stiffness model of the spline with the finite element (FE) model of the rotor system, a dynamic model of a gear-rotor-bearing system is developed. The analysis shows that the contact force, contact angle, and system vibration are only affected when the spalling is located in load-bearing areas. The misalignment of the outer ring leads to the increase of the load-bearing area range of the bearing and the influence probability of the spalling on the system.

Aiming to improving the out-of-plane instability of I-steel arches in large-section tunnels, this study conducted the full-scale test of a single arch, the numerical test of the arched frame structures formed by the longitudinal connections and the arches, and the field comparison test. The results indicated that the failure mode of the single arch was local out-of-plane instability, leading to a loss of overall bearing capacity. The in-plane bearing capacity and out-of-plane stability of arched frame structures considering longitudinal connection bearing capacity are enhanced. In addition, the bearing capacity of the primary support can be fully utilized by adjusting the longitudinal connection spacing and the arch spacing to improve the internal force sharing ratio of the arched frame structure and the shotcrete. However, the longitudinal connection spacing should be less than 1500 mm, and the arch spacing should be less than 1200 mm. Therefore, without changing the existing structural form of the primary support, the arched frame structures with spatial bearing effect formed by rationally arranged longitudinal connections and arches can not only ensure the bearing capacity of the primary support, but also improve construction efficiency and economic benefits. The research findings can guide the structural design of primary support for large-section tunnels.

The effective length coefficient of the pier (ECP) is important for both the stability and the strength of the piers. The ECP of multi-span continuous rigid-frame bridge is calculated by a new model and the corresponding semi-analytical solution method in order to solve the stability of the bridge pier. Firstly, a general mechanical model of the n-span rigid-frame bridge is established, and its characteristic equation for the in-plane stability under consideration of self-weight load is derived using the transfer matrix method (TMM). The elastic buckling load and the ECP are obtained, and are compared with the results acquired by the finite element method to verify the correctness of the proposed theory and method. At the same time, the ECP is investigated when the pier is reinforced by carbon fiber reinforced polymer (CFRP) and ultra-high performance concrete (UHPC), respectively. Additionally, the effects of the ratio of side span to mid span, deck girder stiffness and pier stiffness on the ECP are also explored. The results show that enhancing the stiffness of the overall structure is more effective than enhancing that of the local structure to improve stability, and the ECP is affected significantly by the variation of side span or mid span. Interestingly, a unique bimodal effect is also observed in the ECP curves with the change in the CFRP reinforcement height.

A new large deformation and increasing resistance anchor cable was developed. The energy absorption and pressure release were achieved through connecting six straight tube-shaped steel structures (thickness of 5 mm) containing a circular V-shaped groove in series, with the energy absorption ratio of 44.55 J/g. The pull-out experiment indicates that the ultimate deformation (221.58 mm) of the new anchor cables is 4.87 times larger over that of traditional anchor cables, achieving good properties of large deformation, increasing resistance and high energy absorption. Through secondary development of the universal discrete element code (UDEC), two elastic deformation stages of the supporting resistance — deformation curves for anchor cables were simulated. The numerically simulated supporting effects of the new anchor cables on deep-buried roadways show that the roof subsidence decreases by 88.33% and 74.64%, the peak maximum principal stress at stable states declines by 23.15% and 18.34%, and the thickness of plastic zones decreases by 37.50% and 62.50%, respectively, compared with those of the roadways with no support and traditional anchor cable support. Finally, the new-developed anchor cables were successfully applied in real roadways, with the maximum convergence deformation for the two sides of approximately 300 mm, achieving a good supporting effect.

Based on the Taiyuan Railway Station underpass tunnel project, the influence of construction process of closed pipe-roof pre-construction structures on the ground settlement was investigated. Numerical simulations were used firstly to analyze the ground settlement characteristics caused by three types of different jacking pipe sequences, i. e., from top to bottom, simultaneous construction bottom and top, and bottom to top with nine cases. Numerical simulation results show that the top-down jacking pipe sequence caused the least amount of ground settlement at 12 mm. The largest amount of ground settlement of 25 mm was caused by using the bottom-up jacking pipe sequence. The numerical simulation results were validated by large scale model tests. The results of the model tests agree with the numerical simulation results, with the top-down jacking pipe sequence causing the least ground settlement and the bottom-up jacking pipe sequence causing the most ground settlement. Based on numerical simulation and model tests results, the reasonable jacking pipe sequence was successfully applied in the north tunnel of Taiyuan Railway Station to meet the settlement requirements. The results of the research show that micro soil arches are formed between adjacent jacked pipes in the jacking pipe construction. The micro soil arches between adjacent pipes above the tunnel combine into a large pipe soil arch structure, which can reduce the ground settlement caused by the jacking pipe under the tunnel and on both sides. Therefore, the sequence of jacking pipe considering a pipe soil arch structure can reduce the ground settlement caused by the jacking pipe.

The slip-shear failure type of footwall slope is a type of beding slope that often appears in mining engineering, which has the characteristics of strong suddenness and extensive failure range. How to quickly and accurately define the plastic disturbed zone of excavation and evaluate its stability is vital for safety control. In this work, the failure mode and characteristics of this type of slope are first revealed by numerical simulation tests. Then, according to the failure mode of the slope, considering the uniaxial compressive strength of the rock mass, the mathematical equation describing the excavation disturbed zone is established. Finally, a new mechanical truncation method (MTM) is proposed to calculate the excavation disturbed zone and stability of the footwall slope. It is found that the MTM can accurately characterize the disturbed zone. The calculated limit cutting depth, disturbance thickness, and safety factor are in good agreement with the numerical simulation results, and the evaluation results are safer than numerical simulations. The maximum thickness of the disturbed zone determines the depth of the anchor end of the anchor cable. The disturbed zone indicates the critical area for reinforcement and provides engineering construction and monitoring guidance for the footwall slope.

To achieve scientific and accurate support for the roadway roof in the N00 mining method for thin coal seams, the roof-cutting self-forming roadway is divided into two stages: the advanced chamber stage (Stage I) and the roof collapse and roadway formation stage (Stage II), considering its technological process and the characteristics of roof deformation. Using the Hoek-Brown nonlinearity rock mass strength failure criterion, we derive the formula for the required pre-tension force of anchor bolts/cables at different stages of the roof. Additionally, a design approach is proposed for determining the necessary pretension force and length of anchor bolts and cables. Moreover, the supporting mechanism of anchor bolts/cables and the impact of different supporting combinations on the stress distribution of the surrounding rock are obtained through numerical simulations, elucidating the influence of key parameters in the design of anchor bolts/cables on roof stability. Finally, the partition compensation support technology (PCST) is introduced, and the design principles for anchor bolts and cables on the roof are established. Furthermore, this innovative support technology is implemented at Xintai Coal Mine, yielding favorable results in field applications.

Rock strength and joint parameters are the basic parameters reflecting engineering rock quality. The traditional rock strength testing method requires taking cores from the surrounding rock on site and transporting them to the laboratory for testing. It is difficult for the test results to reflect the mechanical properties of rock in an engineering site environment. In this paper, the relationship between rock cutting energy density and drilling parameters is established, a prediction model of rock equivalent strength based on drilling parameters (ES-DP model) is constructed, and systematic rock digital drilling tests are carried out. The test results show that the average difference rate between rock equivalent compressive strength measured by the drilling test is 2.4% compared with traditional test methods. On this basis, the identification model of rock joint parameters based on drilling is established. The average accuracy of the rock joint position and width measured by the model is 1.8 and 1.6 mm, respectively. Based on the above research, an identification method for rock strength and joint while drilling is proposed in this paper. It provides a new method for simultaneous in-situ testing of the strength parameters and structural characteristics of surrounding rock in underground engineering.

Carbon dioxide (CO₂) geological sequestration is an effective way to control CO₂ emissions, and the geological safety in CO₂ injection project is the most concern problem. Enzyme-induced carbonate precipitation (EICP) technique is believed as useful to overcome CO₂ leakage problem, but its main cementation matter, calcium carbonate, may be corroded by acidic CO₂ solution. Therefore, laboratory studies are necessary to investigate the acid corrosion and resistance of EICP treated sandy soils. In this study, the EICP specimens were immersed in acid solutions with different concentrations, and both mechanical strength and micro-macro structure were investigated based on mass loss, apparent analysis, unconfined compressive strength tests, SEM and XCT. The results indicate that the corrosive effect of acid solution on EICP specimens was obviously strengthened by the decrease in solution pH, the ablation of calcium carbonate destroyed the cementation-pore structure resulting in the gradual shedding of the outer layer of the specimens and the nearly linear decrease in unconfined compressive strength. After acid corrosion reaction, the EICP specimens were found with a large number of intergranular pores among calcium carbonate particles. This study reveals the evolution mechanism of acid corrosion of EICP specimens, providing a reference for the corrosion resistance of EICP.

Combined with the backfill mining, the heat collection tube group (HCTG) in the backfill body can extract geothermal energy, which can effectively alleviate heat damage caused by high ground temperature. This paper takes the HCTG as research object, the temperature, velocity and pressure distribution of the heat transfer fluid (HTF) during the heat release process of the backfill body were analyzed, and the influences of Re, tube diameter, tube spacing and tube arrangement on the performance of the HCTG were discussed. The results show that the heat transfer capacity increases from 2.24×10³ kJ to 16.78×10³ kJ and the comprehensive evaluation factor increases from 0.087 to 1.31 for Re from 100 to 5000. The heat transfer capacity increases from 15.07×10³ kJ to 17.11×10³ kJ and the comprehensive evaluation factor increases from 1.157 to 1.388 for tube diameter from 4 mm to 6 mm. The heat transfer capacity increases from 14.24>10³ kJ to 16.25>10³ kJ and the comprehensive evaluation factor increases from 1.013 to 1.263 for tube spacing from 130 mm to 170 mm. In addition, the four-way parallel arrangement can ensure higher heat transfer capacity and lower pressure drop, and obtain a higher comprehensive evaluation factor. The research provides a theoretical reference for the design and optimization of HCTG in the backfill body.

Direct current internal resistance (DCR) is a key indicator for assessing the health status of batteries, and it is of significant importance in practical applications for power estimation and battery thermal management. The DCR of lithium-ion batteries is influenced by factors such as environmental temperature, state of charge (SOC), and current rate (C-rate). In order to investigate the influence of these factors on battery DCR, this paper proposes a DCR dynamic model of lithium-ion battery based on multiple influencing factors (multi-factor). The model utilizes a binary quadratic polynomial to perform least squares fitting of the DCR with respect to environmental temperature and battery SOC. The obtained coefficients of the binary quadratic polynomial are then fitted with a cubic polynomial with respect to the C-rate, thus establishing the relationship between DCR and C-rate, environmental temperature, and SOC. Multi-rate hybrid pulse power characterization (HPPC) experiment is conducted to perform charging-discharging tests on lithiumion batteries. The experimental results demonstrate that the RMSE between the estimated DCR obtained from the established model and the experimental values is 0.9758 mΩ, confirming the effectiveness of the proposed DCR model.