Changming Zhang

Harmonic drive is susceptible to strength failure and performance degradation failure during operation. Given the long life test cycles, limited sample size, and incomplete understanding of degradation laws, this study conducted comprehensive life test and performance degradation test research to enable future failure prediction and reliability assessment for harmonic drive. Building upon established test rigs for a HD life test and performance degradation test, a step-down accelerated life test methodology was developed. Life tests under step-down accelerated conditions were executed, with a concurrent performance degradation test throughout the life test. Key datasets acquired include vibration signal histories, degradation data for critical performance indicators such as stiffness, precision, transmission efficiency, and backlash. Test results show that the predominant strength failure in the atmospheric environment is flexspline fatigue fracture, while significant degradation occurred in stiffness, precision, and backlash across all test conditions; transmission efficiency showed gradual degradation before strength failure followed by a marked decline post-failure. Finally, the failure mechanism of strength and performance degradation is analyzed, and the mechanism consistency of the two failures is verified by Hilbert envelope spectrum analysis and degradation trajectory shape consistency, respectively. The results from this paper provide critical data support and a reference foundation for the proactive maintenance of the harmonic drive.

The shock absorbers in the landing gear absorb and dissipate a significant amount of kinetic energy generated from impacts during the landing and taxiing phases to ensure the stability and safety of the aircraft. The nitrogen–oil binary system is a commonly used energy absorption medium in these shock absorbers. Nevertheless, the interplay of interfacial mass transfer dynamics, microscopic dissolution behavior, and pressure drop in the aviation hydraulic oil–N₂ system under landing conditions necessitates further elucidation. Thus, we investigated the interfacial mass transfer characteristics of the oil–gas mixing process using molecular dynamics (MD) for analyzing the dissolution mechanism of N₂ in the aviation hydraulic oil system. The results show that as system pressure and temperature increase, the degree of oil–gas mixing intensifies. Under conditions of 373 K, 35 MPa and 433 K, 20 MPa, the diffusion coefficient, interfacial thickness, and system energy reach their maximum values. An increase in system pressure facilitates the occurrence of oil–gas mixing until the interface disappears at the minimum miscibility pressure (MMP), with the obtained MMP value being 107 MPa. Finally, the solubility of N₂ molecules in aviation hydraulic oil under different conditions was statistically analyzed, which is identified as the root cause of the pressure drop in the shock absorber’s gas chamber. This study innovatively applies molecular dynamics simulations to unveil, for the first time, the dissolution mechanism of N₂ in aviation hydraulic oil at the molecular scale, overcoming experimental limitations in observing extreme pressure–temperature conditions. This research elucidates the behavior of aviation hydraulic oil and N₂ under different thermodynamic conditions, making it easier to capture the patterns of phenomena that are difficult to observe in extreme environments. The research findings not only enhance the microscopic understanding of oil–gas mixing within the shock absorber but also provide valuable guidance for optimizing energy dissipation efficiency, improving damping characteristics, and enhancing safety in aircraft landing gear systems.

By adjusting the fluorine content and the molar ratio of 4,4'-dicyclohexylmethane diisocyanate (HMDI) to isophthalaldehyde (IPAL), a novel fluorinated polysiloxane/polyurea (FPUI) with an optimized dual-healing network of hydrogen and imine bonds is synthesized. Using FPUI as a low-surface-energy matrix and incorporating nano-SiO₂ via spraying, a biomimetic fluorinated polysiloxane/polyurea-silica (FPUS) anti-icing coating is developed, achieving durable anti-icing and de-icing performance. FPUS demonstrates complete self-healing within 15 min at room temperature, with tensile strength, elongation at break, and shear strength of 1.43 MPa, 159.32%, and 1.14 MPa, respectively. Water droplets on FPUS-coated surfaces (glass, carbon steel, plastic, and rubber) exhibit significantly longer freezing times compared to uncoated substrates. For instance, on uncoated glass, water freezes in 27 s, whereas on FPUS-coated glass, freezing is delayed to 619 s. Additionally, ice adhesion strength on uncoated glass is 364.16 kPa but was drastically reduced to 23.25 kPa on FPUS-coated glass. Even after 10 freeze-thaw cycles, the adhesion strength remained stable, increasing only slightly to 26.65 kPa. Beyond its anti-icing capabilities, FPUS also exhibited self-cleaning, antibacterial, and anti-corrosion properties. These features make it a promising candidate for protecting outdoor infrastructure and engineering equipment, such as wind turbine blades, photovoltaic panels, power transmission lines, aircraft, and offshore oil platforms.