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The deleterious consequences of hydrogen on an engineering structure come about through an influence on either the crack initiation or the slow crack growth stage of fracture. Whether or not these two stages of fracture are affected by hydrogen will depend on a number of primary and secondary influences which severely complicate the embrittlement process. In this review we present a somewhat phenomonological overview of the hydrogen embrittlement process, both internal as well as external, in an effort to make more clear the type of parameters which must be considered in the selection of a test method and test procedure such that the resulting data may be meaningfully applied to real engineering structures. We consider what are believed to be the three primary influences on the embrittlement process: (1) the original location and form of the hydrogen, (2) the transport reactions involved in the transport of hydrogen from its origin to some point where it can interact with the metal to cause embrittlement, and (3) the embrittlement interaction itself. Additionally, a few of the large number of secondary influences on the embrittlement process are discussed, for example, the influence of impurity species in the environment, surface hydride films, and surface oxide films. Finally, specific test procedures are discussed in order to further elucidate the parameters which must be considered in the development of a standardized test method.
hydrogen embrittlement, crack propagation, parameters, engineering structures, voids, cyclic loads, tests
Ames Research Center, National Aeronautics and Space Administration, Moffett Field, Calif.