Prediction of Strength Degradation at Aging of Pristine Silica Optical Fibers

Abstract

Strength degradation of pristine silica optical fibers immersed in water at stress-free condition, i.e., “aging”, is believed to result form the roughness development of corroded glass surface. This study has investigated in detail the geometrical properties of the roughness development. High-resolution topography was obtained by atomic force microscopy for aged samples. Simulations of surface roughening were also conducted by means of stochastic differential equation for heterogene-ous dissolution of silica. The experiments and simulations suggested that (1) the corroded surface has self-affine geometry, where the Hurst exponent is kept to 0.85 during the roughness development, (2) the roughening is caused by fluctuations of dissolution rate of silica, and (3) the roughness increases in a power law of aging time with an exponent of 0.8. Boundary element stress analyses for the self-affine surface was also carried out to obtain a relationship between the roughness and the strength, where the surface process layer was introduced to prevent difficulties concerning on stress singularity and the stress concentration factor was adopted as a fracture parameter.