Fracture analysis of rubber sealing meterial for high pressure hydrogen vessel

In order to clarify the influence of high pressure hydrogen gas on mechanical damage in a rubber O-ring, the fracture analysis of the O-ring used for a sealing material of a pressure hydrogen vessel was conducted. The O-ring was exposed twenty cycles to hydrogen gas at 100 MPa. All the cracks observed in this study emanated from the interior, which can be classified into two types, type 1 and type 2, from the viewpoint of the location of crack initiation and the direction of crack growth. The type-1 cracks started from the center of the O-ring, while the type-2 cracks started from the sites near the surface of the O-ring. It is implied that tensile stress by squeezing influenced crack initiation and growth of the type-1 cracks. The mechanical damage by the type-1 cracks was more serious than that by the type-2 cracks. Stress analysis was conducted by the nonlinear FEM; then fatigue crack initiation of the O-ring was evaluated in terms of the maximum principal strain criterion, which has been widely employed for the evaluation of fatigue strength of rubber materials. The strain generated by squeezing was considerably smaller than fatigue fracture strain although the increase in the strain due to swelling was considered. It is considered that the type-1 cracks initiated and grew due to strain concentration caused by bubbles which were formed from supersaturated hydrogen molecules after decompression in addition to the strain due to squeezing and swelling.