Anelastic Behavior of Silicate Glass-Ceramics and Partial Melts: Migration of the Amorphous Phase

Abstract

The majority of the residual glass in a silicate glass-ceramic or the melt phase in a silicate partial melt resides in the prismatic triple junction channels that are interconnected throughout the two-phase body. This morphology allows the aggregate to have a dilatational viscosity. Application of a differential stress requires that the local melt fraction reestablish structural equilibrium with the hydrostatic (mean-normal) component of the stress state. In the case of compressive σ₁, the melt is driven to a free surface or to portions of the specimen having lower compressive potential. The melt flow can be rate limited by either the viscosity of the melt phase, or by the ability of the solid residuum to accommodate the triple junctions as they shrink or grow. Removal of the stress requires the “back flow” of the melt phase; the phenomenon is clearly anelastic. This coupled fluid mechanics problem, which has applications ranging from melt migration and seismic wave attenuation in Earth’s mantle to the transient creep response of ceramic composites, has been characterized in creep and fatigue experiments in both compressional and flexural loading configurations. The results of experiments on, and the development of numerical models for an enstatite glass-ceramic (EGC) undergoing four-point flexure are presented and interpreted.