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It is now more than 100 years since certain detrimental effects on the ductility of iron were first associated with the presence of hydrogen. Not only is hydrogen embrittlement still a major industri al problem, but it is safe to say that in a mechanistic sense we still do not know what hydrogen (but not nitrogen or oxygen, for example) does on an atomic scale to induce this degradation. The same applies to other examples of environmentally-induced fracture: what is it about the ubiquitous chloride ion that induces premature catastrophic fracture (stress corrosion cracking) of ordinarily ductile austenitic stainless steels? Why, moreover, are halide ions troublesome but the nitrate or sulfate anions not deleterious to such stainless steels? Likewise, why are some solid metals embrit tled catastrophically by same liquid metals (liquid metal embrit tlement) - copper and aluminum, for example, are embrittled by liquid mercury. In short, despite all that we may know about the materials science and mechanics of fracture on a macroscopic scale, we know little about the atomistics of fracture in the absence of environmental interactions and even less when embrittlement phe nomena such as those described above are involved. On the other hand, it is interesting to note that physical chemists and surface chemists also have interests in the same kinds of interactions that occur on an atomic scale when metals such as nickel or platinum are used, for example, as catalysts for chemical reactions.
Papers in the proceedings of the 32nd U.S. Symposium on Rock Mechanics were solicited to address the theme of 'Rock Mechanics as a Multidisciplinary Science'. The major goal was to assemble scientists and practitioners from various fields with interrelated interests in rock mechanics to share their common problems and approaches. The proceedings include three papers related to a special session on 'Lunar Rock Mechanics', as well as 121 technical papers covering areas such as: field observations, in-situ stresses, instrumentation/measurement techniques, fracturing, rock properties, dynamics/seismicity, modelling, laboratory testing, discontinuities/fluid flow, design, wellbore stability, and analysis.
The theme of the 31st US Symposium on Rock Mechanics is 'Rock Mechanics contributions and challenges', having as objective the examination and quantification of the progress that has been achieved in addressing the major practical challenges facing the science of rock mechanics and mine design. The 124 papers included in the proceedings cover areas such as: experimental studies (laboratory and field); conceptual, analytical, and numerical modeling; design and construction methods. 35 papers deal with practical mining problems and include information on rock reinforcement technology, blasting, rock bursts, open pit mining, remote sensing and borehole geophysics, mechanical fragmentation, and subsidence. Areas emphasized are coal and metal mine design problems. Other papers deal with the newest computer models, new instruments, fracture mechanics, new laboratory testing techniques, and in situ testing.
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
For many years it has been recognized that engineering materials that are-tough and ductile can be rendered susceptible to premature fracture through their reaction with the environment. Over 100 years ago, Reynolds associated hydrogen with detrimental effects on the ductility of iron. The "season cracking" of brass has been a known problem for dec ades, but the mechanisms for this stress-corrosion process are only today being elucidated. In more recent times, the mechanical properties of most engineering materials have been shown to be adversely affected by hydrogen embrittlement or stress-corrosion cracking. Early studies of environmental effects on crack growth attempted to identify a unified theory to explain the crack growth behavior of groups of materials in a variety of environments. It is currently understood that there are numerous stress-corrosion processes some of which may be common to several materials, but that the crack growth behavior of a given material is dependent on microstructure, microchemistry, mechanics, surface chemistry, and solution chemistry. Although the mechanism by which various chemical species in the environment may cause cracks to propagate in some materials but not in others is very complex, the net result of all environmentally induced fracture is the reduction in the force and energy associated with the tensile or shear separation of atoms at the crack tip.
Semiannual, with semiannual and annual indexes. References to all scientific and technical literature coming from DOE, its laboratories, energy centers, and contractors. Includes all works deriving from DOE, other related government-sponsored information, and foreign nonnuclear information. Arranged under 39 categories, e.g., Biomedical sciences, basic studies; Biomedical sciences, applied studies; Health and safety; and Fusion energy. Entry gives bibliographical information and abstract. Corporate, author, subject, report number indexes.