Mechanisms of the Transition in Static Fatigue of Pristine Silica Optical Fibers

点击翻译按钮获取中文摘要

The study aims to clarify a mechanism of"transitions" in static fatigue of pristine silica optical fibers under a stress and to present a method of predicting the phenomenon. The transition is a turning point where a trend in strength degradation of fibers changes abruptly. The research results are summarized as follows:1. Preliminarily we investigated an aging behavior of fibers in liquid water at 90 ℃, where the aging is a strength degradation under no stress and is recognized as a phenomena very close to the transitions. Atomic force microscopy (AFM) for aged surfaces of fibers showed that the surface roughness grows in proportion to a power of aging time but the profile keeps a self-affined fractal with a Hurst' index of 0.85. We also simulated aging of fiber based on a stochastic differential equation (SDE) taking account of a fluctuation of dissolution rate of silica. The simulations were able to explain the experimental results qualitatively. This insists that aging is caused by … More a fluctuation of dissolution rate. Stress analysis for aged surface profiles also showed that a stress concentration factor is a key parameter to predict aging of fibers.2. We simulated growth of surfaces roughness for fibers under a constant stress by using SDE It is found form the simulations that a main crack develops quickly and the crack growth controls lifetime of fibers at high stress conditions before transitions, but roughness developments dominates at low stress conditions after transitions.3. Observations of fiber surface profile are useful to predict a remained lifetime of fibers under a service use. To compensate a limited resolutions of AFM, we focused on an apparent contact stiffness between to AFM tip and sample surface. The stiffness must be affected local small roughness inside the contact area. Previously, we developed a special AFM cantilever with its mass concentrated as a way of enhancing the sensitivity in detection of a contact stiffness. In the present study, we produced a method of evaluating an elastic modulus of sample with a lateral resolution of about lOnm quantitatively. This method would be useful to detect a surface roughness of atomic levels. Less