Fatigue properties of liner materials used for 35MPa-class on-board hydrogen fuel tanks

To evaluate mechanical properties of the materials used for hydrogen systems such as fuel cell vehicles and hydrogen fuel stations, mechanical testing facilities in gaseous hydrogen at up to 45MPa pressure were newly designed and installed, and fatigue properties, which is one of the key properties for the onboard fuel tanks in the fuel cell vehicles, were actually evaluated for two kinds of liner materials of the on-board CFRP fuel tanks; AA6061-T6 aluminum alloy and 316L type of austenitic stainless steel. Axial S-N fatigue tests (R=-1) were conducted in air and also in gaseous hydrogen at 45MPa pressure at room temperature, and quite similar S-N curves were obtained in both circumstances within the maximum number of cycles to failure of 105 for AA6061-T6. 316L also exhibited excellent fatigue life and was not fractured with maximum applied stress of 90% of 0.2% proof stress at 105 cysles. Clear difference was not observed in fatigue crack growth rate in each material regardless of the circumstances investigated in this study including hydrogen gas at 45MPa pressure. Those results indicate that fatigue properties are not affected by gaseous hydrogen at around room temperature in both AA6061-T6 aluminum alloy and 316L type of stainless steel, and that both materials can fully be employed to the liner of the 35MPa on-board hydrogen fuel tanks from the viewpoints of fatigue properties.