The Effect of Hydrogen on the Fatigue Properties of Austenitic Stainless Steel
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The Effect of Hydrogen on the Fatigue Properties of Austenitic Stainless Steel Adam L. Nekimken,1 Patrick D. Ferro,1 John A. Sousa,1 Christine K. Ngan,1 Michael D. Phillips,1 and Chauncy N. Cullitan2 1 Mechanical Engineering Department, Gonzaga University, 502 E Boone, Spokane WA, 99258 2 Physics Department, Gonzaga University, 502 E Boone, Spokane WA, 99258
ABSTRACT Hydrogen can be used as an environmentally friendly fuel to power vehicles, electric devices, and spacecraft with water vapor as the only emission. One associated challenge is the development of safe hydrogen storage systems. Hydrogen tanks and other hydrogen infrastructure elements will be exposed to both high-pressure hydrogen and cyclic stresses. In our work, 304 stainless steel specimens were precharged with hydrogen and subjected to rotational bending fatigue with a maximum stress amplitude of 90 ksi. A diffusion model was solved to approximate the concentration of hydrogen in the specimen at the time of the test. Contrary to our previous work with simple bending fatigue tests, hydrogen precharging actually increased rotational bending fatigue life from 28,074 (Sx = 7,430, N = 103) cycles to 91,513 (Sx = 40,209, N=32) cycles, a factor of approximately 3.25. This result demonstrates that the effect of hydrogen on fatigue life can be highly situational, and great care should be taken when designing systems that will be exposed to high-pressure hydrogen under fatigue conditions. INTRODUCTION Concerns about the global impacts of climate change have generated a push to develop alternative energy systems that have less carbon dioxide emissions compared to traditional combustion. Hydrogen energy technologies have emerged as a key solution. One challenge associated with the development of these technologies is the effects of hydrogen exposure on engineering materials. Hydrogen embrittlement is known to reduce the ductility of structural steels [1, 2]. Brittle materials can be dangerous because they are prone to failure without warning, while ductile materials exhibit plastic deformation that can both stop crack propagation and be used as an indicator of a part’s impending failure [3]. Additionally, fatigue failure in brittle materials occurs slightly differently than ductile materials, with cracks forming at discontinuities and then propagating, rather than first forming slip bands [4]. While the existence of hydrogen embrittlement is well known, the mechanism by which the phenomenon affects mechanical properties is not definitively known. A leading theory, hydrogen-enhanced localized plasticity (HELP), purports that hydrogen increases the mobility of dislocations by locally softening the material at the crack tip [5]. Austenitic stainless steels tend to have better performance compared to other structural steels when exposed to hydrogen [6]. Murikami et al. [7] found that, contrary to expectation, hydrogen can actually increase the fatigue life of stainless steel. They propose that this is the result of a pinning mechanism where hydrogen locally increase
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