## 5 Conclusions  
1. In this study, a finite element model of the axial propulsion combined seal structure is established. Compressive stress-strain curves of EPDM at \(-\)60 \({}^{\circ}\)C, 15 \({}^{\circ}\)C, and 130 \({}^{\circ}\)C are obtained through uniaxial compression tests, and material parameters for the EPDM constitutive model at three temperatures are determined through fitting. The numerical simulations of the combined sealing structure provide valuable insights, revealing that the stress concentration of the O-ring is similar in both the inflation and deflation states at 15 \({}^{\circ}\)C and 70 MPa, but the sealing performance of the O-ring in the inflation state is better than that in the deflation stage. 2. The investigation into the sealing performance of the combined sealing structure under extreme working conditions reveals significant findings. Compared with the inflation state at 15 \({}^{\circ}\)C and 70 MPa, the maximum von Mises stress is reduced by 65% at 130 \({}^{\circ}\)C and 87.5 MPa, the maximum contact pressure of contact surfaces I and II is reduced by 40%, and the effective sealing lengths of contact surfaces I and II are both reduced by approximately 20%. Conversely, the von Mises stress is increased by 7 times in the deflation state at \(-\)60 \({}^{\circ}\)C and 56 MPa, and the maximum contact pressure on contact surfaces I and II is increased by a remarkable 7 times, with the effective sealing length of contact surface I doubling. Figure 18: Influence of gasket thickness on O-ring performance: (**a**) max von Mises stress; (**b**) max contact pressure. 3. The investigation into the influence of gas pressure on the sealing performance of the combined sealing structure at 15 \({}^{\circ}\)C reveals significant findings. The von Mises stress of the O-ring increases significantly in both the inflation and deflation state, but the increase is more rapid in the deflation state. Interestingly, the increase in gas pressure (10-100 MPa) has a negligible influence on the sealing performance of contact surface I in the deflation state, while significantly improving the sealing performance of the other three conditions (contact surface I inflation, contact surface II inflation, and contact II deflation). 4. The investigation into the influence of gasket parameters on the sealing performance of the combined sealing structure at 15 \({}^{\circ}\)C and 70 MPa reveals significant findings. Increasing the gasket thickness can effectively reduce the stress concentration of the O-ring, but excessive gasket thickness (more than 0.9 mm in this study) will aggravate the stress concentration. The maximum contact pressure of contact surface I in the deflation state is significantly improved, while the effect of gasket thickness on the sealing performance of contact surface II in the deflation state is negligible. Based on the influence of gasket thickness on von Mises stress and contact pressure, the optimal range is determined to be between 0.85 mm and 1.05 mm. Within this range, the stress concentration of the O-ring is lighter, resulting in better sealing performance for the combined sealing structure. In addition, the friction coefficient of the gasket surface and the fillet of gasket have negligible influence on the structural performance of the combined sealing structure. In this paper, the performance changes of an EPDM rubber O-ring under extreme working conditions are obtained. The stress concentration phenomenon of the EPDM rubber O-ring is lighter under high temperature conditions, but the sealing performance is decreased. At low temperatures, the stress concentration is serious, but the sealing performance is better. These conclusions provide reference for the selection of rubber materials for extreme temperature environments. Additionally, the influence of the gasket fillet, gasket thickness, gasket surface friction coefficient, and working pressure on the sealing performance of the combined sealing structure are analyzed.