Effects of high pressure hydrogen gas on the fatigue strength for long-term use in candidate materials for the fuel cell system

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In order to ensure the safety of materials of a fuel cell system against long-term fatigue in high pressure hydrogen gas environment, it is necessary to clarify the characteristics of hydrogen entry into the material and the effects of internal hydrogen and hydrogen gas on the fatigue characteristics and the fatigue mechanisms.(1) Measurements of hydrogen content in SCM 435 show that a plasma-charged sample contains 0.25 ppm hydrogen, which is 5 times in non-charged sample. The hydrogen plasma has ability as an alternative of high- pressure gas hydrogen environment However, the data are spread. Discussion of another plasma generation method or measures against heat evolution is required.(2) Fatigue life of plain specimen cannot explain the effects of hydrogen gas environment, because hydrogen gas lengthen the fatigue crack initiation life, while shorten the fatigue crack propagation life.(3) Degree of fatigue crack acceleration by hydrogen is different among materials: SUS304, SUS316L, SUS310S and A6061-T6.(4) Slip-off mechanism is valid even in hydrogen gas environment in a certain range of fatigue crack growth.(5) It is considered that the traditional assessment technique for the fatigue crack growth based on slip-off is effective and addition of the effects of diffusion rate to the assessment technique is a next object.