Hongjuan Yan

Aiming at satisfying the micro-dynamic lubrication requirements of moving parts in spacecraft on-orbit operation, this paper proposes a micro-oil supply scheme based on a piezoelectric drive. The working mode and transient sound pressure characteristics of the micro-oil supply device were analyzed by the numerical simulation method, and the influence of driving voltage and oil dynamic viscosity on droplet growth and desorption behavior was investigated. The research results show the following: (1) The driving voltage is a key external control parameter that affects the droplet ejection characteristics. The increase of its amplitude will promote the droplet morphology to change from a stable and concentrated overall state to a dispersed state with multi-satellite droplets and easy necking fracture. At the same time, the droplet size is significantly reduced, the distribution tends to be discretized and the droplet velocity and droplet mass are simultaneously improved. Under the 220 V voltage condition, the droplet ejection velocity can reach 17.8 m/s, and the single ejection mass can reach 6.98 mg, which can realize the rapid and large-scale delivery of droplets. (2) Dynamic viscosity is the core intrinsic parameter to determine the droplet ejection characteristics. When the value of dynamic viscosity increases, the droplet morphology will change from the wire-like fracture characteristics of ‘spherical head + satellite droplet developed’ to the droplet-like structure with overall concentration and stable mechanical state. The average droplet size increased and the distribution was more aggregated. The droplet velocity and droplet mass decreased significantly. When the viscosity increased to 0.16 Pa·s, the droplet ejection velocity decreased to 1.14 m/s, and the single ejection mass decreased to 0.35 mg.

This study focuses on porous polyimide (PPI) lubricating materials for high-speed aerospace bearings. Based on their real microstructure, three-dimensional digital model reconstruction and mesoscale seepage characteristics were investigated. First, a sequence of two-dimensional slice images of PPI was obtained using micro-focus X-ray computed tomography (CT). Through image filtering, threshold segmentation, and three-dimensional reconstruction, a highly faithful digital model of the pore structure was constructed, and a quantified pore-network model was further extracted. Second, a multiple-relaxation-time lattice Boltzmann model based on the D3Q27 discrete scheme was established, and its accuracy and stability in complex boundaries and pressure-driven flows were verified using classic benchmark cases. Subsequently, the validated numerical model was applied to the reconstructed PPI pore structure to simulate and systematically analyze the single-phase seepage behavior of lubricating oil. The results show that the lubricant seepage exhibits a strong “preferential flow path” effect, with most of the flow transported through a small number of large-size throats. A clear quantitative relationship exists between the microscopic flow field structure—including velocity distribution, flow paths, and pressure gradient—and the pore-topology features, such as throat-size distribution, connectivity, and tortuosity. This verifies the mesoscale mechanism that “structure governs flow.” The complete technical chain established in this work—“real-structure reconstruction–numerical model validation–seepage mechanism analysis”—provides a reliable theoretical and numerical tool for gaining deeper insight into the lubricant transport behavior in porous polyimide and offers guidance for the microstructural design and optimization of this material.

Defective graphene has emerged as a promising strategy to enhance electrochemical performance of pristine graphene (p-Gr) as anodes in lithium-ion batteries (LIBs). Herein, we perform a comprehensive first-principles study based on density functional theory (DFT) to systematically investigate the Li adsorption, charge transfer, and diffusion behaviors of p-Gr and defective graphene (d-Gr) with single vacancy (SV Gr) and double vacancy (DV5-8-5 Gr) defects, aiming to clarify the mechanism by which defects modulate Li storage performance. Structural optimization reveals that SV Gr undergoes notable out-of-plane distortion after Li adsorption, while DV5-8-5 Gr retains planar geometry but exhibits more significant C-C bond length variations compared to p-Gr. Binding energy results confirm that defects enhance Li adsorption stability, with DV5-8-5 Gr showing the strongest Li–graphene interaction, followed by SV Gr and p-Gr. Bader charge analysis and charge density difference plots further validate that defects enhance charge transfer from Li ions to graphene. Using the nudged elastic band (NEB) method, we find that defects reduce Li diffusion barriers: DV5-8-5 Gr exhibits a lower barrier than p-Gr. Our findings demonstrate that DV5-8-5 Gr exhibits the most favorable Li storage performance, providing a robust theoretical basis for designing high-performance graphene anodes for next-generation LIBs.

During the machining of nickel-based superalloys using coated tools, a significant amount of cutting heat is generated. This study employs ABAQUS finite element analysis software to establish two-dimensional orthogonal cutting simulation models for three types of coated tools: single-layer AlTiN, double-layer AlTiN/AlCrN, and AlCrN/AlTiN. The research focuses on simulating the cutting temperature and cutting stress of carbide tools with these three different coating types and thicknesses when machining nickel-based superalloy GH4169. The simulation results indicate that the double-layer AlCrN/AlTiN-coated tool exhibits lower maximum cutting temperature and cutting stress on the tool rake face and tool substrate during the cutting process. Compared to the other two coated tools, the cutting temperature and cutting stress on the rake face are reduced by up to 13.2% and 13.3%, respectively. When the AlCrN/AlTiN coating thickness is 2.5 μm with a ratio of 1.5:1, the maximum cutting temperature and cutting stress are minimized. During the cutting process with coated tools, the cutting speed, coating type, and coating thickness significantly influence the maximum cutting temperature and cutting stress. Therefore, investigating the effects of cutting speed, coating type, and coating thickness on carbide-coated tools can reduce tool wear, extend tool life, and thereby improve machining efficiency.

The impact of modulation periods on the microstructure, as well as the tribological and mechanical characteristics of the AlCrTiVNbN/TiSiN nano multilayer films, was investigated. The films were prepared with modulation periods ranging from 4 nm to 7 nm, and their properties were explored using X-ray diffraction (XRD), scanning electron microscope (SEM), nanoindentation, and a tribological tester. All nano multilayer films revealed a face-centered cubic (FCC) structure with a preferred planar direction of (200). As the modulation period increased, the XRD peak moved to higher angles, and the interplanar distance decreased. Also, the mechanical properties deteriorated, and the COF rose monotonically as a result. The nano multilayer film with a modulation period equal to 4 nm exhibited a smooth surface with minimal small particles, the highest hardness of 15.51 ± 0.16 GPa and elastic modulus of 182.89 ± 2.38 GPa, the highest values for the ratios of H/E and H³/E², the lowest average friction coefficient of 0.73, and a wear rate equal to (8.2 9 ± 0.18) × 10⁻⁸ mm³·N⁻¹·m⁻¹. The improvement in the properties of the film was ascribed to the coherent growth and alternating stress field between the AlCrTiVNbN and TiSiN layers.

Titanium alloys are difficult to machine and have poor tribological properties. Nanoparticles have good cooling and lubricating properties, which can be used in metal cutting fluid. The lubrication characteristics of the two-dimensional materials Ti₃C₂T_X MXene and graphene oxide in water-based fluid for titanium alloys were comparatively investigated in this paper. Graphene oxide had smaller friction coefficients and wear volume than Ti₃C₂T_X MXene nanofluid. As to the mechanism, MXene easily formed TiO₂ for the tribo-chemical reaction, which accelerated wear. Moreover, GO nanofluid can form a more uniform and stable friction layer between the frictional interface, which reduces the friction coefficient and decreases the adhesive wear. The effects of different surfactants on the lubricating properties of MXene were further investigated. It was found that the cationic surfactant Hexadecyl trimethyl ammonium chloride (1631) had the lowest friction coefficient and anti-wear properties for the strong electrostatic attraction with MXene nanoparticles. The results of this study indicate that 2D nanoparticles, especially graphene oxide, could improve the lubricating properties of titanium alloys. It provides insight into the application of water-based nanofluids for difficult-to-machine materials to enhance surface quality and cutting efficiency. The developed nanofluid, which can lubricate titanium alloys, effectively has very broad applications in prospect.

The SOC estimation of UAV lithium batteries plays a crucial role in the mission planning and safe flight of UAVs. Aiming at existing UAV lithium battery SOC estimation problems, such as low estimation accuracy and poor real-time performance, a real-time online estimation scheme for UAV lithium battery SOC is proposed. A model-based approach is adopted to establish an SOC estimation model on the basis of the Thevenin equivalent circuit model, and a UAV lithium battery online monitoring device is developed to monitor the current and voltage of the UAV lithium battery in real time and import the data into the SOC estimation model in real time for calculation. Using the developed online monitoring device, the current and voltage of the lithium UAV battery are monitored in real time, and the data are imported into the SOC estimation model in real time for calculation, realizing the real-time online estimation of the SOC of the lithium UAV battery. The experimental results show that the program can realize the real-time online estimation of UAV lithium battery SOC, and the estimation error is less than 3%, which meets the requirements of online estimation accuracy of the UAV lithium battery SOC.

Titanium alloys are difficult to machine and have poor tribological properties. This paper investigates the lubricating performance of γ-Al₂O₃/ZnO hybrid nanofluids for Ti-6Al-4V. Pure and hybrid nanofluids are compared, and the effects of γ-Al₂O₃/ZnO ratios are studied. The results show that γ-Al₂O₃/ZnO hybrid nanofluids outperform pure nanofluids in terms of lower friction coefficients and better surface quality. Moreover, the hybrid nanofluid with a mass ratio of Al₂O₃ to ZnO of 2:1 demonstrates the best lubrication performance with a reduced friction coefficient of up to 22.1% compared to the base solution, resulting in improved surface quality. Al₂O₃ nanoparticles can adhere to the surface of ZnO nanoparticles and work as a coating, which further enhances the lubrication performance of the water-based nanofluid.

Titanium alloys are difficult to machine and have poor tribological properties. This paper investigates the lubricating performance of γ-Al2O3/ZnO hybrid nanofluids for Ti-6Al-4V. The pure and hybrid nanofluid are compared, and the effects of γ-Al2O3/ZnO ratios are studied. The results show that γ-Al2O3/ZnO hybrid nanofluids outperform pure nanofluid in terms of lower friction coefficients and better surface quality. Moreover, the hybrid nanofluid with a mass ratio of Al2O3 to ZnO of 2:1 demonstrates the best lubrication performance with a reduced friction coefficient of up to 22.1% compared to the base solution, resulting in improved surface quality. Al2O3 nanoparticles can adhere to the surface of ZnO nanoparticles and work as a coating, which further enhances the lubrication performance of the water-based nanofluid.

In order to explore the effect of modulation period on the structure and properties of TiSiN/NiTiAlCoCrN nanomultilayer films, the films were deposited on 304 stainless steel via a magnetron sputtering system. The structure and element distribution of the films were observed via X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The cavitation erosion of the films was investigated using an ultrasonic vibration cavitation machine. The results show that the TiSiN/NiTiAlCoCrN nanomultilayer film exhibits a face-centered cubic (FCC) structure and preferred orientation on the (200) crystal plane. TiSiN/NiTiAlCoCrN nanomultilayer films grow in the form of columnar crystals, which grow perpendicularly to the direction of the substrate. With increasing modulation periods, the hardness, elastic modulus, and adhesive force firstly increase and then decrease. When the modulation period is 11 nm, the TiSiN/NiTiAlCoCrN nanomultilayer film has the biggest hardness of (14.649 ± 0.591) GPa, elastic modulus of (249.065 ± 10.485) GPa, and adhesive force of 11.3 N. With increasing modulation periods, the mass loss firstly decreases and then increases. When the modulation period is 11 nm, the mass loss is the minimum of 0.6 mg. There are two reasons for improving the cavitation erosion resistance of the films. The TiSiN/NiTiAlCoCrN nanomultilayer film has the highest hardness, and the interfaces of the nanomultilayer film can hinder the generation and expansion of cavitation pits.