KYUDAI NEWS KYUSHU UNIVERSITY CAMPUS MAGAZINE Spring 2014 No.25

15/28

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In fact, it is for the rst time that such a formula has been proposed that describes the hydrogen effect on fatigue acceleration in terms of the important parameters that govern this complex phenomenon of fatigue crack growth.We are working on the development of a model to simulate fatigue crack growth by accounting for the effects of hydrogen on crack tip plasticity. The model involves hydrogen adsorption kinetics in the presence of an oxide lm forming on the freshly created surfaces at the crack tip. Using nite element analysis to simulate hydrogen induced crack growth, our goal is to develop a predictive relationship for the crack growth rate in terms of the environment, material, and loading parameters. In addition, we plan to use rst principles calculations to understand how hydrogen competes with oxygen or other unsaturated compounds for adsorption sites on a free surface. In the case of hydrogen-accelerated fatigue failure, we do not understand how relatively low pressures of hydrogen can markedly degrade the material resistance to cyclic loading. In general, assessing component lifetime, developing mitigation or remediation strategies, or designing smart structural materials for employment in a hydrogen environment is one of the main goals of I2CNER. To achieve this, an international team from world premier universities and laboratories has been assembled. It is a team of experts in Materials Science and Microstructural characterization (Dr. Somerday from Sandia National Laboratres, Prof. Robertson from the University of Wisconsin-Madison), Materials Physics (Prof. Kirchheim from the University of Gottingen), Computational Science (Prof. Staykov of I2CNER), Tribology (Prof. Sugimura from Kyushu University), and Alloy Development (Prof. Takaki from Kyushu University).Hydrogen embrittlement is a severe environmental type of failure that can cause a sudden and catastrophic failure under loads a component can sustain in the absence of hydrogen. Although the phenomenon of hydrogen-induced degradation of metals and alloys is well documented, there remains a paucity of information about the wide spectrum of pathways through which hydrogen degrades the material properties and how these depend on the in-service conditions. Describing quantitatively the fundamentals of the hydrogen/deformation interactions and fracture mechanisms is central to the development of methodologies and tools for material performance prognosis in order to i) assess the resistance of existing materials to hydrogen embrittlement and ii) design intelligently new materials that are not susceptible to hydrogen embrittlement over a wide range of operating conditions. A very important outcome of this work is an experimentally validated formula that describes the amount of oxygen needed to mitigate the hydrogen effect under cycling loading at Professor Petros SofronisDirector, International Institute for Carbon-Neutral Energy Research(I2CNER) Professor, University of Illinois at Urbana-Champaign14Kyudai News No.25 acceleration igate embrittlement Technological issuesNew AchievementFuture prospectsPublicationsTitle:Elucidating the variables affecting accelerated fatigue crack growth of steels in hydrogen gas with low oxygen concentrationsAuthors:B. P. Somerday, P. Sofronis, K. A. Nibur, C. San Marchi, R. KirchheimJournal:Acta Materialia, Vol. 61, pp. 6153-6170, 2013.Dr. Brian Somerday, Sandia National LaboratoriesProfessor Reiner Kirchheim, University of Göttingen

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