## 7 Conclusions  
In this study, the mechanical behavior and sealing capacity of the gasket-in-groove were studied using experiments, and the numerical FEA model validated by the test  
Figure 13: The maximum contact pressure path at the gasket–gasket contact surface with different initial maximum contact pressure.  
results was used to further investigate thoroughly the sealing behavior and sealing failure mechanism of the gasket-in-groove. The following conclusions can be drawn:  
1. The numerical model presented in this paper can model the fluid permeation state at the gasket contact surface and thus predict the airtightness of the gasket-in-groove. Furthermore, the numerical model can provide assistance to engineers in the analysis of gasket sealing performance and the optimization of gasket parameters at a lower time and cost.
2. The experimental and numerical study results show that the load-displacement curve of the gasket-in-groove has a significant nonlinear behavior, and it can be roughly categorized into three stages according to the maximum gasket compression.
3. The FEA results are in good agreement with the experimental results. This implies that the finite element model established in this paper captures the nonlinear behaviors of the gasket well, but the comparisons with experimental tests indicate it may overestimate the sealing capacity of the gasket-in-groove.
4. The FEA results show that the air leakage of the gasket-in-groove occurs on the gasket-gasket contact surface due to a lower maximum contact pressure compared to that on the gasket-groove contact surface.
5. The FEA results show that the initial contact pressure distribution on the gasket-gasket contact surface is symmetrically distributed in a \"W\" shape, with a layout of higher at the ends and lower in the middle, and a smaller joint gap would result in higher contact pressure.
6. The FEA results show that a higher \(p_{imax}\) would provide a better sealing effect. The higher initial maximum contact pressure will lower the ratio of \(p_{s}/p_{imax}\) and \(p_{f}/p_{imax}\), and the lower \(p_{f}/p_{imax}\) would lead to a lower factor of safety of the sealing for a given initial maximum contact pressure.
7. The FEA results show that the vacuum pressure significantly affects the contact pressure distribution on the contact surface. Specifically, it shows an overall decreasing trend with the increases in vacuum pressure, and the decreasing rate on the side close to the vacuum pressure is significantly higher than the one away from the vacuum pressure.
8. As the vacuum pressure increases, MCP tends to rise sharply, followed by a slow drop, and then decline dramatically to 0, which mechanistically provides a good illustration of the sealing failure process at the contact surface.  
Conceptualization, D.W. and L.S.; methodology, J.Z. and L.S.; software, L.S.; validation, L.S. and K.C.; formal analysis, J.Z. and L.S.; investigation, D.W. and L.S.; resources, L.S. and K.C.; data curation, K.C.; writing--original draft preparation, L.S.; writing--review and editing, D.W. and L.S.; visualization, J.Z. and L.S.; supervision, D.W.; project administration, D.W.; funding acquisition, D.W. and J.Z. All authors have read and agreed to the published version of the manuscript.  
This work was supported by an open research project grant (# SKLST-2019-K04) from the State Key Laboratory of Shield Machine and Boring Technology.  
Not applicable.  
The data are available from the corresponding author on reasonable request.  
The authors declare no conflict of interest.