Rheology of grain-boundary sliding and grain interlocking

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(1) A novel rheological test system which operates at high temperatures (ranging from 500 to 1300 degree centigrade) was designed and constructed.(2) Theoretical considerations and quantitative derivations were made for the viscoelastic constitutive equations of polycrystals with grain-boundary melt-phase in various types of multiaxial stress/strain fields. The equations include the elastic deformation of respective polycrystalline grains, as well as viscous flow of melt-phase in grain channels.(3) A novel microstructural model for the superplastic deformation of refractory grain aggregates was proposed. The importance of cooperative motions of groups of grains in an aggregate was emphasized to be essential for including a large-scale deformation under tension/compression. An important theoretical prediction for a size-effect law in superplastic deformation was made.(4) Various types of rheological test were conducted by the use of ZrO2-ceramics, and the test results were related to the microscopic processes and mechanisms of grain-boundary Zener-relaxation, grain interlocking, cooperative grain-boundary sliding.(5) Time-dependent viscoelastic surface deformation produced by a pyramidal indentation was theoretically examined to derive a constitutive equation for a microscopic surface contact.(6) A novel indentation test system that operates at elevated temperatures (from 300 to 1500 degree centigrade) was designed, constructed, and applied to rheologically testing various types of inorganic glasses above their glass transition points.