This paper presents the effects of hydrogen pressure, ambient temperature and pressure cycle pattern on fracture behavior of O-rings moulded from a peroxide-crosslinked EPDM rubber with white reinforcing filler under cyclic exposure to high-pressure hydrogen gas. By using a developed durability tester which enables the O-rings to expose cyclically high-pressure hydrogen gas, pressure cycle tests were performed at hydrogen pressures ranging from 10 to 70. MPa and ambient temperatures ranging from 30 to 100. °C under two pressure cycle patterns (test frequencies). The cyclic hydrogen exposure caused cracks in the O-rings, and their crack damage became more serious with an increase in the hydrogen pressure and the ambient temperature. The serious crack damage under high temperature is believed to be due to degradation of mechanical properties with increasing ambient temperature. At a hydrogen pressure of 10. MPa, cracks (blisters) caused by bubbles formed from supersaturated hydrogen molecules after decompression were observed. At a hydrogen pressure of 35. MPa or more, a large volume increase of the O-rings was observed by swelling; then, its volume increase induced extrusion fracture of the O-rings in addition to blister fracture. The crack damage also became more serious with a decrease in test frequency. The effect of the test frequency on the crack damage of the O-rings is presumed to be attributed to time-dependent crack growth behavior of the EPDM rubber.
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