Experiences from Embedded Optical Fiber Based Cure and Stress Sensing in Composite Structures

Abstract

We report here on experiencies with optical fiber embedding and cure monitoring in a composite container manufacturing process, and with external stress measurements. Microbending loss in long single-mode and multi-mode telecommunication fibers was investigated. The measurements were carried out using the optical through power technique and a commercial optical time domain reflectometer. Simple miniature size electronics, applicable even for embedding was developed for example as an alarm indicator. We found that the coating material and its thickness have an effect on loading sensitivity and on the applicability of the method for cure monitoring. Though we discovered that repeatability issues are a problem, the measurement data indicate that the end of the curing process of the composite can be determined by optical sensing fibers. Further, sensing fibers in different wall layers can be used to follow the progress of the curing inside the wall at different depths. The response of damaging external loading on the structure can also be detected.