Surface structural relaxation of silica glass: a possible mechanism of mechanical fatigue

• Published in: Journal of non-crystalline solids 2004-10, Vol.345-346 (Complete), p.449-460
• Main Authors: Tomozawa, Minoru, Hepburn, Robert W.
• Format: Article
• Language: English
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2004.08.065

The mechanical strength of glasses decreases with increasing time of a tensile stress application in the presence of a moist atmosphere. This mechanical fatigue of silica glasses is an important concern when long time usage of a silica glass product is intended, as in the case of silica glass optical fibers. Various different mechanisms of mechanical strength degradation have been proposed but questions still remain. It is proposed here that surface structural relaxation of the glass may be the mechanism of the mechanical fatigue, since the structural relaxation at low temperature produces glasses with lower mechanical strength. Compared with bulk structural relaxation, surface structural relaxation can take place much more rapidly. The kinetics of the surface structural relaxation of silica glass optical fibers (and plates) was investigated using the IR reflection method at various temperatures as a function of water vapor and applied stress. The kinetics of the surface structural relaxation was accelerated by water vapor pressure as well as by applied tensile stress. The results showed that the surface structural relaxation is a possible mechanism of mechanical fatigue.