SURFACE RELAXATION AS A MECHANISM OF STATIC FATIGUE OF PRISTINE SILICA GLASS-FIBERS

Mechanical strength degradation of glass under static stress, or stati c fatigue, is usually attributed to the slow growth. of a surface flaw . But some glasses, such as pristine silica optical fibers, can be mad e free from any surface flaw and yet they exhibit static fatigue. Sinc e pristine glass possesses no crack to grow, an alternative mechanism is needed to explain the static fatigue. Surface structural relaxation is proposed as a fatigue mechanism of such materials. Tensile stress- accelerated surface relaxation kinetics in moist atmosphere were analy zed to obtain the activation volume and the proposed surface relaxatio n mechanism was shown to be plausible. (C) 1998 Elsevier Science B.V. All rights reserved.