Published: Jan 1982
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Two national energy programs are considering caverns in geological salt (NaCl) as a storage repository. One is for the disposal of nuclear wastes and the other is for the storage of oil. Both short-time and long-time structural deformations and stresses must be predictable for these applications. At 300 K, the nominal initial temperature for both applications, the salt is at 0.28 of the melting temperature and exhibits a significant time-dependent behavior. A constitutive model has been developed that describes the behavior observed in an extensive set of triaxial creep tests. Analysis of these tests showed that a single deformation mechanism seems to be operative over the stress and temperature range of interest so that the secondary creep data can be represented by a power of the stress over the entire test range. This simple behavior allowed a new unified creep-plasticity model to be applied with some confidence. The resulting model recognizes no inherent difference between plastic and creep strains yet models the total inelastic strain reasonably well including primary and secondary creep and reverse loadings. A multiaxial formulation is applied with a back stress. A Bauschinger effect is exhibited as a consequence and is present regardless of the time scale over which the loading is applied. The model would be interpreted as kinematic hardening in the sense of classical plasticity. Comparisons are made between test data and model behavior.
creep, unified, constitutive, model, primary, secondary
Member, Technical Staff, Sandia National Laboratories, Albuquerque, N.M.