Fretting Characteristics of Rubber X-Ring Exposed to High-Pressure Gaseous Hydrogen

The rubber ring is an essential component of high-pressure hydrogen storage systems. However, the fretting damage can lead to the seal failure of the rubber ring, which may cause hydrogen leakage. Rubber X-ring has been proven to own excellent static sealing performance, while its fretting characteristics under high-pressure hydrogen remain unclear. In this study, a numerical model is developed to explore the fretting characteristics of the X-ring combined seal, in which the effect of hydrogen swelling is well considered. The stress distribution of the fretting seal and the effects of fretting amplitude, friction coefficient, hydrogen pressure, and pre-compression ratio on the fretting behavior of the X-ring are investigated. Moreover, the similarities and differences in the fretting performance of X-ring and O-ring under high-pressure hydrogen are discussed. It is shown that the evolution of the stress concentration zone inside the X-ring is closely linked to the cover's drag direction and the wedge-ring's blocking action. The X-ring enters the fretting cycle earlier with increased fretting amplitude, whereas the fretting period remains unchanged. Furthermore, increasing the hydrogen pressure and pre-compression ratio could enhance the fretting sealing performance. The friction coefficient and hydrogen pressure increase the possibility of failure due to cracks or elasticity. The fretting characteristics of the X-ring are superior to those of the O-ring, denoting that X-ring may be an alternative to the O-ring in the fretting seal structure. This work is of theoretical importance for the quantitative evaluation and reliable prevention of fretting damage to rubber rings and improving the safety of high-pressure hydrogen storage systems.