Fatigue crack growth experiments and interrupted tests are conducted on the fourth-generation powder metallurgy superalloy FGH4108 under varying temperatures and dwell time. The influence of temperature and dwell time on crack growth behavior is analyzed using characterization techniques such as Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), and Electron Probe Microanalysis (EPMA). The mechanism by which oxidation damage affects crack growth is revealed. A fatigue crack growth rate model describing the mechanical-oxidation coupling effect is proposed. The results show that as temperature and dwell time increase, the crack growth rate rises and fatigue life decreases significantly. Fractographic analysis reveals that at 650 ℃, fatigue cracks primarily propagate transgranularly with relatively flat fracture surfaces, while at temperatures above 750 ℃, fatigue cracks mainly propagate intergranularly, accompanied by the formation of secondary cracks. Concurrently, phenomena such as alterations in crack tip morphology and oxide formation were observed during crack propagation, elucidating the impact of oxidation on crack growth. The proposed model can better describe the fatigue crack growth rate at different temperatures and dwell time. At the same time, the effects of mechanical damage and oxidative damage on crack growth are decoupled, and the temperature dependence of oxidative damage parameters is determined.

To meet the requirements of load-bearing and special environmental adaptability, the envelope of near-space operational aerostats consists of multiple layers, such as high-performance fiber fabrics, helium barrier layers, weather layers, and adhesive layers. Since the internal pressure inside the envelope directly determines load-bearing capacity of the aerostat, it is necessary to develop a reliable constitutive model to predict the equivalent mechanical properties of the envelope, which therefore, lays the foundation for strength and life evaluations of the airship. Effects of fiber fabrics and functional layers on the equivalent mechanical properties of the envelope were investigated by experimental characterizations. Based on experimental results, an equivalent constitutive model was developed to study the anisotropic and nonlinear mechanical behavior of the envelope. For both uniaxial and off-axis tensile conditions, predictions on the effective stress, yarn shear angle and specimen cross-sectional contraction agree well with experimental results. The combined experimental and numerical studies have led to insightful understanding between the overall mechanical response and microstructure deformation of the envelope.