Effect of Hydrogen Gas on the Fatigue Strength of Candidate Material for Fuel Cell System

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In order to know the guide to the rational design for the components under fatigue loading in the fuel cell system, some candidate materials were tested in air, in hydrogen gas and in nitrogen gas at the pressure of below 1MPa. Main results obtained are as follows.1.Austenitic stainless steels SUS304 and SUS316L(1)The effect of hydrogen on the rength of material is not clearly seen in strain-fatigue life diagram.(2)Initiation life in hydrogen gas or in nitrogen gas is longer than that in air(3)Hydrogen gas accelerates the crack growth rate. The degree of acceleration in SUS304 is higher than that in SUS316L(4)Brittle facets on the fracture surface of SUS304 increase in hydrogen gas, however ductile transgranular fracture surface is predominant So it seems that the acceleration occurs in the ductile fracture surface. The facets do not clearly increase in SUS316L.(5)Observation of striation on the fracture surface and the deformation behavior of crack tip, it seems that slip bands at the crack tip in hydrogen gas easily concentrate. The concentration of slip bands plays an important role for the acceleration of crack growth rate.(6)The effect of hydrogen gas on the fatigue limit is not clearly seen.2.Aluminum alloy A6061-T6The effects of pre-strain on the fatigue characteristics of aluminum alloy A6061-T6 in air were investigated. The main results obtained are as follows.(1)Slip bands and cracks occur due to pre-strainaring prior to the fatigue tests.(2)The effect of pre-strain on the fatigue life is not clearly seen.(3)The pre-strain affects the behavior of crack initiation or crack growth. The effect of pre-strain in hydrogen gas environment on the fatigue characteristics is a problem to be solved in near future.