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

本研究的目的是澄清一个机制的“过渡”在静态疲劳的原始石英光纤在应力下，并提出了一种方法来预测的现象。该转变是纤维强度退化趋势突然改变的转折点。主要研究成果如下：1.首先，我们研究了纤维在90 ℃液态水中的老化行为，其中老化是无应力下的强度退化，被认为是非常接近于转变的现象。原子力显微镜（AFM）的老化纤维表面显示，表面粗糙度的增长与老化时间的幂成比例，但轮廓保持自仿射分形与赫斯特指数为0.85。我们还模拟了基于随机微分方程的光纤老化，考虑到二氧化硅的溶解速率的波动。模拟能够定性地解释实验结果。这坚持认为衰老是由 ...更多信息 溶解速率的波动。对老化表面轮廓的应力分析也表明应力集中因子是预测纤维老化的关键参数.利用ANSYS软件模拟了恒定应力下纤维表面粗糙度的增长过程，发现在过渡前的高应力条件下，主裂纹发展迅速，裂纹增长控制纤维的寿命，而在过渡后的低应力条件下，粗糙度发展占主导地位.纤维表面形貌的观察有助于预测纤维在使用过程中的剩余寿命。为了弥补原子力显微镜有限的分辨率，我们专注于原子力显微镜针尖和样品表面之间的表观接触刚度。接触区域内的局部小粗糙度必然会影响刚度。在此之前，我们开发了一种特殊的AFM悬臂，其质量集中作为一种方式，提高灵敏度检测的接触刚度。在本研究中，我们提出了一种方法，定量评估样品的弹性模量的横向分辨率约为10纳米。该方法可用于检测原子级的表面粗糙度。少

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