Rheology of grain-boundary sliding and grain interlocking at high temperatures

A two-dimensional array of elastic hexagonal grains embedded in an contiguous fluid is used as a model for grain-boundary sliding and grain interlocking. The viscoelastic constitutive equation, in a phenomenological sense, is of a nonlinear Maxwell type, comprising a strain-dependent dashpot and an elastic spring connected in series. The squeezing-in/out processes and mechanisms of grain-boundary fluid essentially give rise to the rheological nonlinearity. The experimental results in stress relaxation tests of a beta-spodumene glass-ceramic under simple shear are characterized in a light of the nonlinear constitutive equation. It is emphasized that stress relaxation test is one of the important test techniques which enable one to study quantitatively the rheological behavior of polycrystalline ceramics with grain-boundary sliding and grain interlocking without any difficulties and ambiguities accompanied by stress-induced grain-boundary cavities which so often appear in conventional creep tests.