| 講演要旨： |
In April of 2003, Energy Secretary Abraham summarized the new hydrogen economy by stating that consumers will have the practical option of purchasing a competitively priced hydrogen power vehicle, and be able to refuel it near their homes and places of work by 2020. However, the technology of large scale hydrogen transmission from central production facilities to refueling stations and stationary power sites is at present undeveloped. Among the problems which confront the implementation of this technology is the deleterious effect of hydrogen on structural material properties, in particular at gas pressure of 1000 psi which is the desirable transmission pressure suggested by economic studies for efficient transport. Despite extensive study over almost a century, a complete mechanistic understanding of the hydrogen-induced degradation of engineering materials has yet to be achieved. Our current understanding leads to the recognition that there is no single mechanism causing hydrogen embrittlement. Of the many suggestions, three mechanisms appear to be viable: stress-induced hydride formation and cleavage, hydrogen-enhanced localized plasticity, and hydrogen-induced decohesion. To understand these mechanisms of embrittlement our approach integrates mechanical property testing at the micro and macroscale, microstructural analyses and TEM observations of the deformation processes at the micro- and nano-scale, thermodynamic considerations for the material cohesive properties at the atomistic scale, and finite element modeling and simulation at the micro- and macro-level. It is demonstrated that hydrogen i) enhances dislocation mobility by shielding the interactions between microstructural defects; ii) induces loss of ellipticity in the governing rate equations of the macroscopic elastoplastic material response which is manifested in the onset of severe shear localization of the plastic flow; iii) can reduce both the macroscopic stress and strain for internal void nucleation and grain boundary decohesion. A discussion will be presented on how we can develop and verify a lifetime prediction methodology for failure of materials used in pipeline systems and welds exposed to high-pressure gaseous environments. Development and validation of such predictive capability and strategies to avoid material degradation is of paramount importance to the rapid assessment of the suitability of using the current natural-gas pipeline distribution system for hydrogen transport, as has been recommended by the National Research Council, and of the susceptibility of new alloys tailored for use in the new hydrogen economy. |
