Fatigue behavior of polyimide coated optical fibers at elevated temperatures

Abstract

As optical fiber is being used in much harsher environments than traditional telecommunications (e.g. distributed temperature sensing at elevated temperatures) understanding its mechanical properties at high temperatures is urgently needed. As a continuation of our previous work on high temperature strength of silica optical fiber, we report our results in fatigue behavior of polyimide coated silica optical fiber at 300°C in this paper. Fiber fatigue is the degradation in strength caused by a stress dependent chemical reaction between water vapor and the surface of the silica glass. In contrast to the published data on degradation in mechanical properties of silica optical fiber at elevated temperatures, our observations indicate a negligible decrease in strength along with unchanged, n-value, (fatigue resistant factor) at 300°C. To determine the n value, we tested tensile strength of the fiber using four different strain rates while the subject under test was at 300°C. The results indicate that the polyimide coating on the silica glass fiber continues to serve as an effective water vapor barrier at 300°C. These results will be compared with data available for room temperature performance of this silica/polyimide combination and possible failure mechanisms will be discussed.