Sealing rings are the core components of flange sealing structures and play a crucial role in the storage and operation of gas generators. The aging and deformation of seals affect the safe operation of the device. This paper aims to investigate the effect of rubber aging on the sealing performance of the components, which is realized by nonlinear finite element analysis. Firstly, an accelerated degradation test method was used to obtain the compression permanent deformation and stress–strain curve of rubber during the aging process. A two-dimensional finite element model of the sealing structure was constructed and the Yeoh model was utilized to describe the mechanical response of rubber. During the simulation, the contact area was modified based on the compression permanent deformation, and the Yeoh model was updated based on the stress–strain curve changes obtained by the test. The impact of key parameters such as material property changes, rubber physical section deformation, and fluid pressure on sealing performance during the seal ring aging process was systematically studied. The numerical results indicate that due to the aging deformation of rubber seals, there is a significant decrease in contact stress and contact width, as well as a shift in maximum equivalent stress area. Taking into account these findings, this study proposes a new design concept for sealing structures. This provides a relatively simple research method for studying flange sealing structure performance.

In order to study the influencing factors of friction coefficient in an M-B model, based on the basic model of fractal theory, the distribution function and probability distribution density of the micro-convex body truncation area are derived by using mathematical and statistical means, and a new model of critical truncation area and friction coefficient in fractal surface contact process are proposed. Considering the differences between the actual contact area and the truncated area during plastic deformation of the micro-convex body, a correction factor is introduced. Focusing on the mechanism of the elastic-plastic transition phase, and finally a friction coefficient model based on the fractal dimension, the normal force and correction factor is derived. Finally, the friction coefficient of fractal surface is simulated and verified by taking nickel as an example, and it is proved that the new model is correct in predicting the change trend of friction coefficient in the M-B model.

In the field of aerospace, weapons and other complex assembly, there are more than 50 factors affecting the performance degradation of joint structures, among which the friction coefficient is the main factor. Nickel steel is widely used in large complex equipment due to its advantages of high strength. Therefore, this paper first establishes a theoretical model of friction coefficient based on fractal theory. Secondly, the friction coefficient experiment was carried out to measure the friction coefficient of nickel steel plates with different roughness under different normal loads. Finally, the experimental results are compared with the theoretical results, and the accuracy and error analysis of the model is carried out. The results show that the friction coefficient increases with the increase in roughness. When the normal load is greater than 50 kg, the friction coefficient gradually tends to be stable. The error of identification results of correction factor a was all within 5%. The error between theoretical model prediction and experimental data is 6%–15%, which indicates that the calculation of the friction coefficient has high accuracy. The results of this study can provide data and theoretical support for the friction coefficient evaluation of nickel steel plate joint structures, and contribute to the health detection and reliability evaluation of nickel steel plate joint structures.

The mechanical properties of silicone foam will degrade when exposed to environmental loads such as temperature and pressure for a long time. In recent years, the variation law of the stress–strain response of silicone foam during the aging process has received more and more attention, but there are few works that quantitatively analyze the variation of the stress–strain response. In this work, we quantitatively analyzed the variation law of the stress–strain response of silicone foam during aging by the constitutive model. Firstly, the accelerated aging test of silicone rubber foam under long-term compressive strain was carried out, and its compression set, stress relaxation and strain stress curves of different aging degrees were obtained. Further, degenerate trajectory equations for the compression set and stress–relaxation were obtained. In addition, the hyper-foam constitutive model was obtained by fitting stress–strain curves, and the changes in the model parameters after aging were studied. The results show that the compressed set and stress–relaxation are exponential functions of time, while different to existing research findings, we found that the stress–strain curves do not change monotonically with increasing time, which first softens, then hardens, and finally softens. Additionally, to better understand the changing trend of the stress–strain response, the correlation between the stress–strain curve and the compression set and stress–relaxation was discussed qualitatively. Finally, in the stage of monotonic change of the stress–strain curve, the exponential function of the model parameters with the increase of aging time was obtained.

Bolted joints, with their advantages of simple structure and convenient disassembly and assembly, are widely used in complex equipment fields such as aerospace systems and weaponry. Subject to complex mechanical loads, the contact surfaces may undergo nonlinear behaviors such as contact–separation and viscous slip, leading to the nonlinear degradation of the connection stiffness, which severely threatens the safety and reliability. These have driven research on bolted joints to span multiple disciplines, from interfacial micro-friction to macro-structural dynamics. Therefore, from the field of micro-friction to macro-dynamics, this review summarizes and analyzes three major degradation models, outlines the experimental development in connected structures, and provides an overview of the numerical analysis methods for degradation simulation. This paper also looks forward to the development directions for future research on the degradation of connected structures.