High-entropy alloys (HEAs) have become essential materials in the aerospace and defense industries due to their remarkable mechanical properties, which include wear resistance, fatigue endurance, and corrosion resistance. The welding of high-entropy alloys is a cutting-edge field of study that is attracting a lot of interest and investigation from research organizations and businesses. Welding defects including porosity and cracks are challenging problem and limit the development of welding HEAs. This paper provides a comprehensive review of research on weldability of HEAs and the application of diverse welding techniques on welding HEAs over recent years. The forming mechanism and control strategies of defects during welding HEAs were provided in this work. Various welding techniques, including arc welding, laser welding, electron beam welding, friction stir welding, diffusion bonding and explosive welding, have been extensively investigated and applied to improve the microstructure and mechanical properties of HEAs joints. Furthermore, an in-depth review of the microstructure and mechanical properties of HEAs joints obtained by various welding methods is presented. This paper concludes with a discussion of the potential challenges associated with high-entropy alloy welding, thus providing valuable insights for future research efforts in this area.

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High-entropy alloy composites (HEACs) have attracted significant attention due to their exceptional mechanical properties and chemical stability. By adjusting the content of reinforcing particles in the high-entropy alloy and by employing advanced additive manufacturing techniques, high-performance HEACs can be fabricated. However, there is still considerable room for improvement in their performance. In this study, CoCrFeMnNi HEA powders were used as the matrix, and NiCoFeAlTi high-entropy intermetallic powders were used as the high-entropy reinforcement (HER). CoCrFeMnNi/NiCoFeAlTi HEACs were fabricated using selective laser melting technology. The study results indicate that after aging, the microstructure of HEACs with HER exhibits Al- and Ti-rich nano-oxide precipitates with an orthorhombic CMCM type structure system. After aging at 873 K for 2 h, HEACs with HER achieved excellent overall mechanical properties, with an ultimate tensile strength of 731 MPa. This is attributed to the combined and synergistic effects of precipitation strengthening, dislocation strengthening, and the high lattice distortion caused by high intragranular defects, which provide a multi-scale strengthening and hardening mechanism for the plastic deformation of HEACs with HER. This study demonstrates that aging plays a crucial role in controlling the precipitate phases in complex multi-element alloys.

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The research demonstrated that laser powder bed fusion (LPBF) coupled with controlled annealing at 1200 °C, could significantly increase the proportion of coincidence site lattice (CSL) grain boundary, thereby achieving an outstanding synergy of enhanced strength and exceptional ductility. The plastic deformation behavior, strain hardening behavior, and fracture behavior of LPBF 316L steel annealing at 1200 °C for 20 h were studied through quasi-in-situ tensile process. It was found that LPBF 316L steel formed a certain proportion of deformation twins during the tensile process, and the formation of twins changed the crystal orientation, thus promoting further slip and crystal deformation. The synergistic effect of slip and twin promoted higher plasticity. LPBF process coupled with controlled annealing at 1200 °C for 20 h leads to a ultimate tensile strength of 613 MPa and total elongation of 73.8%.

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Laser powder-bed fusion (LPBF) of Zn-0.8Cu (wt.%) alloys exhibits significant advantages in the customization of biodegradable bone implants. However, the formability of LPBFed Zn alloy is not sufficient due to the spheroidization during the interaction of powder and laser beam, of which the mechanism is still not well understood. In this study, the evolution of morphology and grain structure of the LPBFed Zn-Cu alloy was investigated based on singletrack deposition experiments. As the scanning speed increases, the grain structure of a single track of Zn-Cu alloy gradually refines, but the formability deteriorates, leading to the defect’s formation in the subsequent fabrication. The Zn-Cu alloys fabricated by optimum processing parameters exhibit a tensile strength of 157 MPa, yield strength of 106 MPa and elongation of 14.7%. This work provides a comprehensive understanding of the processing optimization of Zn-Cu alloy, achieving LPBFed Zn-Cu alloy with high density and excellent mechanical properties.

In the present study, molecular dynamic simulation (MD) was used to investigate the plastic deformation process of the Fe-Mn alloys with different Mn contents. The influences of Mn contents ranging from 10% to 30% (at%) on the deformation behavior and the controlling mechanism of the Fe-base alloys were analyzed. The results show that phase transformations and {112} <111>_BCC deformation twinning occur in all Fe-Mn alloys but follow different deformation paths. In the Fe-10%Mn alloy the deformation twinning mechanism obeys the FCC-related path, the Fe-20%Mn alloy involves both the FCC- and HCP-related paths, and the deformation of the Fe-30%Mn alloy is dominated by the HCP-related twinning path. The addition of Mn can increase the stacking fault energy and retard the activation of slip systems as well as the formation of stacking faults. Thus, a higher content of Mn can delay the FCC→ε-martensite and the subsequent ε-martensite→BCC phase transition at the intersection of two ε-martensitic bands. Therefore, the addition of Mn alloying element increases the yield strength and reduces the elastic modulus of the Fe-Mn alloys. The formation of deformation twins will contribute to the work-hardening effect and delay the necking and fracture of alloys. It is expected that the results in the present study will provide theoretical reference for the design and optimization of high-performance steels.

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The effect of hot deformation on the quench sensitivity of the 7085 alloy was studied through hardness testing and microstructure characterization. The findings indicate that hot deformation enhances the quench sensitivity of the 7085 alloy, with the hardness difference between water quenching and air cooling increasing from 5.4% (before hot deformation) to 10.4% (after hot deformation). In the undeformed samples, the Al₃Zr particles within the grains exhibit better coherent with the Al matrix. During slow quenching, only the η phase is observed on Al₃Zr particles and at the grain boundaries. Hot deformation leads to a mass of recrystallization and the formation of subgrains with high dislocation density. This results in an increase in the types, quantities, and sizes of heterogeneous precipitates during quenching. In the slow quenching process, high angle grain boundaries are best for the nucleation and growth of the η phase. Secondly, a substantial quantity of η and T phases precipitate on the non-coherent Al₃Zr phase within the recrystallized grains. The locations with high dislocation density subgrains (boundaries) serve as nucleation positions for the η and T phases precipitating. Additionally, the Y phase is observed to precipitate at dislocation sites within the subgrains.

In the present study, two-layered stainless steel-copper composites with a thickness of 50 µm were initially subjected to annealing at 800, 900 and 1000 °C for 5 min, respectively, to achieve diverse microstructural features. Then the influence of annealing temperature on the formability of stainless steel-copper composites and the quality of micro composite cups manufactured by micro deep drawing (MDD) were investigated, and the underlying mechanism was analyzed. Three finite element (FE) models, including basic FE model, Voronoi FE model and surface morphological FE model, were developed to analyze the forming performance of stainless steel-copper composites during MDD. The results show that the stainless steel-copper composites annealed at 900 °C possess the best plasticity owing to the homogeneous and refined microstructure in both stainless steel and copper matrixes, and the micro composite cup with specimen annealed at 900 °C exhibits a uniform wall thickness as well as high surface quality with the fewest wrinkles. The results obtained from the surface morphological FE model considering material inhomogeneity and surface morphology of the composites are the closest to the experimental results compared to the basic and Voronoi FE model. During MDD process, the drawing forces decrease with increasing annealing temperature as a consequence of the strength reduction.

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In the process of protecting ferrous materials, aluminum coating usually forms a dense oxide film on the surface of the iron-based alloy. However, the capacity of the sacrificial anode is rather insufficient. In order to solve this problem, the microstructure and electrochemical corrosion properties of Al-8Si-3Fe-xIn alloy under low chlorine conditions were studied. The results show that indium (In) dissolves to form In³⁺ and In⁺ reverse plating on the surface of the bare substrate to form a passivation film defect. When the In content is high, the segregated In forms an activation point in the form of a cathode phase. In activates τ₆ phase to form a micro-couple, which improves the non-uniform corrosion. The In-containing corrosion products at the phase boundary hinder the diffusion of Cl⁻. With an increase of In content, the self-corrosion potential (E_corr) of the alloy shifts negatively, and the self-corrosion current density (J_corr) decreases from 6.477 µA/cm² to 1.352 µA/cm², and then increases gradually. However, when the In content is 0.1%, the E_corr of the alloy changes from −0.824 V to −0.932 V, and the J_corr decreases from 6.477 µA/cm² to 4.699 µA/cm², suggesting that the use of sacrificial anode will give the best effect.

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As a cathode material for thermal batteries, NiS₂ has a high theoretical capacity but low thermal stability. Besides, the poor formability of NiS₂ powders also restricts the cathode performance of thermal batteries. In this paper, the novel NiS₂/SiO₂ composite material was developed by high temperature vulcanization to improve the thermal stability formability of NiS₂. The good filling and lubrication of spherical SiO₂ can improve the thermal conductivity of NiS₂ electrode. The discharge test shows that the NiS₂/SiO₂ cathode has a stable discharge voltage at a current density of 200 mA/cm², and the activation time is shortened by nearly 20% compared with the NiS₂ cathode. In addition, due to the favorable thermal insulation protection of SiO₂, the initial decomposition temperature of NiS₂ is increased by 30 °C after the addition of SiO₂. The incorporation of SiO₂ not only effectively improves the thermal stability and electrochemical properties of NiS₂, but also improves the cold pressing forming performance of the NiS₂ powder. Therefore, the novel NiS₂/SiO₂ composite material is more suitable for thermal batteries with high stability and fast response, which is of great significance for improving the maneuverability and quality reliability of weapons and equipment.

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Effect of flip chip bonding parameters on microstructure at the interconnect interface and shear properties of 64.8Sn35.2Pb microbumps were investigated in this work. Results show that the main intermetallic compound (IMC) at the interconnect interface is (Ni, Cu)₃Sn₄ phase, and meanwhile a small amount of (Cu, Ni)₆Sn₅ phase with a size of 50–100 nm is formed around (Ni, Cu)₃Sn₄ phase. The orientation relationship of [

](Ni, Cu)₃Sn₄//[152](Cu, Ni)₆Sn₅ and (601)(Ni, Cu)₃Sn₄//(

\overline{2}01

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)(Cu, Ni)₆Sn₅ is found between these two phases, and the atomic matching at the interface of the two phases is low. The highest shear force of 77.3 gf is achieved in the 64.8Sn35.2Pb microbump at the peak temperature of 250 °C and parameter V₁ because dense IMCs and no cracks form at the interconnect interface. Two typical fracture modes of microbumps are determined as solder fracture and mixed fracture. The high thermal stress presenting in the thick IMCs layer induces crack initiation, and cracks propagate along the α/β phase boundaries in the Sn-Pb solder under shear force, leading to a mixed fracture mode in the microbumps.

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Micro- and nano- to millimeter-scale magnetic matrix materials have gained widespread application due to their exceptional magnetic properties and favorable cost-effectiveness. With the rapid progress in condensed matter physics, materials science, and mineral separation technologies, these materials are now poised for new opportunities in theoretical research and development. This review provides a comprehensive analysis of these matrices, encompassing their structure, size, shape, composition, properties, and multifaceted applications. These materials, primarily composed of alloys of transition state metasl such as iron (Fe), cobalt (Co), titanium (Ti), and nickel (Ni), exhibit unique attributes like high magnetization rates, low eleastic modulus, and high saturation magnetic field strengths. Furthermore, the studies also delve into the complex mechanical interactions involved in the separation of magnetic particles using magnetic separator matrices, including magnetic, gravitational, centrifugal, and van der Waals forces. The review outlines how size and shape effects influence the magnetic behavior of matrices, offering new perspectives for innovative applications of magnetic matrices in various domains of materials science and magnetic separation.

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Traditional pyrometallurgical and hydrometallurgical methods to extract bismuth from sulfide ores face problems such as high cost, low-concentration SO₂ generation, and long process time. In this study, the cyclone technology and slurry electrolysis method were combined. The bismuth sulfide ore was dissolved directly at the anode, while the high purity bismuth was deposited efficiently at the cathode under the advantages of the two methods. The short process and high-efficiency extraction of bismuth sulfide ore were realized, and the pollution of low-concentration SO₂ was avoided. Then, the effects of several crucial experimental conditions (current density, reaction time, temperature, pH, liquid-solid ratio, and circulation flow rate) on the leaching efficiency and recovery efficiency of bismuth were investigated. The leaching and electrowinning mechanisms during the recovery process were also analyzed according to the research results of this paper to better understand the cyclone slurry electrolysis process. The experimental results showed that 95.19% bismuth was leached into the acid solution in the anode area under optimal conditions, and the recovery efficiency and purity of bismuth on the cathode reached 91.13% and 99.26%, respectively, which were better than those by the traditional hydrometallurgy recovery process.

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In response to the fact that the presence of manganese dithionate (MnS₂O₆) leads to a series of adverse impacts, especially lower purity of manganese sulfate (MnSO₄) and disruption of its recovery, advanced oxidation methods such as ozonation system are used to manage MnS₂O₆ in the leaching solution, replacing conventional methods. To ascertain the conversion rate and kinetics of MnS₂O₆ during the ozonation process, we explored the factors influencing its removal rate, including ozone dosage, manganese dithionate concentration, sulfuric acid concentration, and reaction temperature. Batch experiments were conducted to determine the reaction rate constant of ozone (k) and activation energy (E_a) obtained from intermittent experimental data fitting, revealing a least-squares exponential conversion relationship between k and the MnS₂O₆ removal amount, wherein an increase in the aforementioned factors led to an enhanced MnS₂O₆ conversion rate, exceeding 99.3%. The formation mechanism of the ozone products proposed during the experiment was summarized and proposed as follows: 1) Mn²⁺ was directly oxidized to MnO₂, and 2) SO₄²⁻ was obtained by the catalytic oxidation of S₂O₆²⁻ with HO• from O₃ decomposition. According to the kinetics analysis, the pre-exponential factor and total activation energy of the ozonation kinetics equation were 1.0×10²³ s⁻¹ and 177.28 kJ/mol, respectively. Overall, the present study demonstrates that O₃ as an oxidizing agent can effectively facilitate MnS₂O₆ disproportionation while preventing the release of the secondary pollutant, SO₂ gas.

Single-atom catalysts (SACs) are promising for oxygen reduction reaction (ORR) on account of their excellent catalytic activity and maximum utilization of atoms. However, due to the complicated preparation processes and expensive reagents used, the cost of SACs is usually too high to put into practical application. The development of cost-effective and sustainable SACs remains a great challenge. Herein, a low-cost method employing biomass is designed to prepare efficient single-atom Fe-N-C catalysts (SA-Fe-N-C). Benefiting from the confinement effect of porous carbon support and the coordination effect of glucose, SA-Fe-N-C is derived from cheap flour by the two-step pyrolysis. Atomically dispersed Fe atoms exist in the form of Fe—N_x, which acts as active sites for ORR. The catalyst shows outstanding activity with a half-wave potential (E_1/2) of 0.86 V, which is better than that of Pt/C (0.84 V). Additionally, the catalyst also exhibits superior stability. The ORR catalyzed by SA-Fe-N-C proceeds via an efficient 4e transfer pathway. The high performance of SA-Fe-N-C also benefits from its porous structure, extremely high specific surface area (1450.1 m²/g), and abundant micropores, which are conducive to increasing the density of active sites and fully exposing them. This work provides a cost-effective strategy to synthesize SACs from cheap biomass, achieving a balance between performance and cost.

Polydimethylsiloxane (PDMS) considered a low surface energy material is widely used in (super)hydrophobic modification. In this paper, the high hydrophobic melamine sponges (MS) were modified with commercial aminopropyl functionalized polydimethylsiloxane (NH₂-PDMS) with different molecular mass. The chemical composition, surface morphology, and wettability of the NH₂-PDMS-modified MS were investigated by X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and contact angle test. Owing to the porous structure and high hydrophobicity, NH₂-PDMS-modified MS possesses remarkable absorption capacity (ranging from 46 to 155 times their own mass). Simultaneously, it can effectively separate oil-water mixtures with high separation efficiencies exceeding 98.2%. NH₂-PDMS-modified MS has no obvious change after 10 cycles of oil-water separation. The results demonstrate PDMS molecular mass on surface can revise material properties and achieve high separation efficiencies in oil-water separation.

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Gear assembly errors can lead to the increase of vibration and noise of the system, which affect the stability of system. The influence can be compensated by tooth modification. Firstly, an improved three-dimensional loaded tooth contact analysis (3D-LTCA) method which can consider tooth modification and coupling assembly errors is proposed, and mesh stiffness calculated by proposed method is verified by MASTA software. Secondly, based on neural network, the surrogate model (SM) that maps the relationship between modification parameters and mesh mechanical parameters is established, and its accuracy is verified. Finally, SM is introduced to establish an optimization model with the target of minimizing mesh stiffness variations and obtaining more even load distribution on mesh surface. The results show that even considering training time, the efficiency of gear pair optimization by surrogate model is still much higher than that by LTCA method. After optimization, the mesh stiffness fluctuation of gear pair with coupling assembly error is reduced by 34.10%, and difference in average contact stresses between left and right regions of the mesh surface is reduced by 62.84%.

To investigate the effects of water and cyclic loading on dolomite’s mechanical properties during deep mining, mechanical experiments on non-pressure water absorption and cyclic loading were conducted. The findings reveal that the elastic modulus and Poisson ratio of dolomite fluctuate with increasing water content. The mass of water absorption is positively correlated with time and the water absorption stage can be divided into three stages: accelerated, decelerated, and stabilized stages. During this process, the number of pores in dolomite increases, while the pore diameter initially decreases and then fluctuates. Microscopic analysis shows that the proportion of mesopores first increases and then decreases, while micropores exhibit the opposite trend, and the proportion of macropores fluctuates around 0%. A model diagram of structural evolution during water absorption has been developed. Additionally, the softening process of dolomite’s water absorption strength is categorized into three stages: a relatively stable stage, an accelerated softening stage dominated by mesopore water absorption, and a decelerated softening stage characterized by micropore water absorption. A uniaxial damage constitutive model for dolomite under water influence was established based on the Weibull distribution and Mohr-Coulomb strength criterion, and experimental validation indicates its strong applicability.

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Narrow backfill earth pressure estimation is applied to study the stability of supporting structures in the vicinity of existing buildings. Previous narrow backfill earth pressure studies have neglected seismic-unsaturated seepage multi-field coupling, resulting in inaccurate estimates. To address these deficiencies, this paper proposed a calculation method for seismic passive earth pressure in unsaturated narrow backfill, based on inclined thin-layer units. It considers the interlayer shear stress, arching effect, and the multi-field coupling of seismic-unsaturated seepage. Additionally, this paper includes a parametric sensitivity analysis. The outcomes indicate that the earthquake passive ground pressure of unsaturated narrow backfill can be reduced by increasing the aspect ratio, seismic acceleration coefficient, and unsaturation parameter α. It can also be reduced by decreasing the effective interior friction angle, soil cohesion, wallearth friction angle, and vertical discharge. Furthermore, for any width soil, lowering the elevation of the action point of passive thrust can be attained by raising the effective interior friction angle, wall-earth friction angle, and unsaturation parameter α. Reducing soil cohesion, seismic acceleration coefficient, and vertical discharge can also lower the height of the application point of passive thrust.

Negative Poisson ratio (NPR) steel is a new material with high strength and toughness. This study conducted tensile tests at elevated temperatures to investigate the mechanical properties of NPR steel at high temperatures. The stress – strain curve, ultimate strength, yield strength, modulus of elasticity, elongation after fracture, and percentage reduction of area of NPR steel bars were measured at 9 different temperatures ranging from 20 to 800 °C. The experimental results indicate that high-temperature environments significantly affect the mechanical properties of NPR steel. However, compared to other types of steel, NPR steel exhibits better resistance to deformation. When the test temperature is below 700 °C, NPR steel exhibits a ductile fracture characteristic, while at 800 °C, it exhibits a brittle fracture characteristic. Finally, based on the experimental findings, a constitutive model suitable for NPR steel at high temperatures is proposed.

Permeable roads generally exhibit inferior mechanical properties and shorter service life than traditional dense-graded/impermeable roads. Furthermore, the incorporation of recycled aggregates in their construction may exacerbate these limitations. To address these issues, this study introduced a novel cement-stabilized permeable recycled aggregate material. A total of 162 beam specimens prepared with nine different levels of cement-aggregate ratio were tested to evaluate their permeability, bending load, and bending fatigue life. The experimental results indicate that increasing the content of recycled aggregates led to a reduction in both permeability and bending load. Additionally, the inclusion of recycled aggregates diminished the energy dissipation capacity of the specimens. These findings were used to establish a robust relationship between the initial damage in cement-stabilized permeable recycled aggregate material specimens and their fatigue life, and to propose a predictive model for their fatigue performance. Further, a method for assessing fatigue damage based on the evolution of fatigue-induced strain and energy dissipation was developed. The findings of this study provide valuable insights into the mechanical behavior and fatigue performance of cement-stabilized permeable recycled aggregate materials, offering guidance for the design of low-carbon-emission, permeable, and durable roadways incorporating recycled aggregates.

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The existing analytical models for umbrella arch method (UAM) based on elastic foundation beams often overlook the influence of the surrounding soil beyond the beam edges on the shear stresses acting on the beam. Consequently, such models fail to adequately reflect the continuity characteristics of soil deformation. Leveraging the Pasternak foundation-Euler beam model, this study considers the generalized shear force on the beam to account for the influence of soil outside the beam ends on the shear stress. An analytical model for the deformation and internal forces of finite-length beams subjected to arbitrary loads is derived based on the initial parameter method under various conditions. The mechanical model of the elastic foundation beam for advanced umbrella arch under typical tunnel excavation cycles is established, yielding analytical solutions for the longitudinal response of the umbrella arch. The reliability of the analytical model is verified with the existing test data. The improved model addresses anomalies in existing models, such as abnormal upward deformation in the loosened segment and maximum deflection occurring within the soil mass. Additionally, dimensionless characteristic parameters reflecting the relative stiffness between the umbrella arch structure and the foundation soil are proposed. Results indicate that the magnitude of soil characteristic parameters significantly influences the deformation and internal forces of the umbrella arch. Within common ranges of soil values, the maximum deformation and internal forces of the umbrella arch under semi-logarithmic coordinates exhibit nearly linear decay with decreasing soil characteristic parameters. The impact of tunnel excavation height on the stress of unsupported sections of the umbrella arch is minor, but it is more significant for umbrella arch buried within the soil mass. Conversely, the influence of tunnel excavation advance on the umbrella arch is opposite.

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Following the fundamental characteristics of the porosity windbreak, this study suggests a new numerical investigation method for the wind field of the windbreak based on the porous medium physical model. This method can transform the reasonable matching problem of the porosity and windproof performance of the windbreak into a study of the relationship between the resistance coefficient of the porous medium and the aerodynamic load of the train. This study examines the influence of the hole type on the wind field behind the porosity windbreak. Then, the relationship between the resistance coefficient of the porous medium, the porosity of the windbreak, and the aerodynamic loads of the train is investigated. The results show that the porous media physical model can be used instead of the windbreak geometry to study the windbreak-train aerodynamic performance, and the process of using this method is suggested.

In this paper, a novel train positioning method considering satellite raw observation data was proposed, which aims to promote train positioning performance from an innovative perspective of the train satellite-based positioning error sources. The method focused on overcoming the abnormal observations in satellite observation data caused by railway environment rather than the positioning results. Specifically, the relative positioning experimental platform was built and the zero-baseline method was firstly employed to evaluate the carrier phase data quality, and then, GNSS combined observation models were adopted to construct the detection values, which were applied to judge abnormal-data through the dual-frequency observations. Further, ambiguity fixing optimization was investigated based on observation data selection in partly-blocked environments. The results show that the proposed method can effectively detect and address abnormal observations and improve positioning stability. Cycle slips and gross errors can be detected and identified based on dual-frequency global navigation satellite system data. After adopting the data selection strategy, the ambiguity fixing percentage was improved by 29.2%, and the standard deviation in the East, North, and Up components was enhanced by 12.7%, 7.4%, and 12.5%, respectively. The proposed method can provide references for train positioning performance optimization in railway environments from the perspective of positioning error sources.

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