Stress Relaxation of Polycrystalline Ceramics with Grain‐Boundary Sliding and Grain Interlocking

Abstract

The stress relaxation of two‐phase polycrystalline ceramics has been examined. A two‐dimensional array of elastic hexagonal grains embedded in a contiguous fluid has been 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; the model is composed of a strain‐dependent dashpot and an elastic spring connected in series. The squeezing‐in/out processes and mechanisms of grain‐boundary fluid essentially result in the rheological nonlinearity. The experimental results in stress‐relaxation tests of a β‐spodumene glass‐ceramic under simple shear are characterized from the standpoint of the nonlinear constitutive equation. It is emphasized that the stress‐relaxation test is one of the important test techniques that enables one to study quantitatively the rheological behavior of polycrystalline ceramics with grain‐boundary sliding and grain interlocking without any of the difficulties and ambiguities that are accompanied by stress‐induced grain‐boundary cavities, which so often appear in conventional creep tests.