Smart textiles: evaluation of optical fibres as embedded sensors for structure health monitoring of fibre reinforced composites

Abstract

Silica optical fibres (SOF) are established for the use of communicating digital data and numerous applications including structure health monitoring. However, SOFs exhibit drawbacks such as brittleness, low strain and signal attenuation due to bending. These drawbacks limit the use of SOF as embedded sensors for monitoring composite structures’ internal health. Unlike SOFs, the relatively newly developed polymer optical fibres (POF) do not possess such drawbacks and they are able to monitor the health of fibre-based composite structures. Bending in optical fibres is a major concern since this causes signal attenuation at bending points. Integrating optical fibres into a woven preform requires bending because of the crimping that occurs as a result of weave interlacing. The main objective of this research was to evaluate the effect of the macrobending of optical fibres on signal power integrity. The goal is to design optical fibre sensors embedded in woven preforms that have high sensitivity for monitoring the health of composite structures. Newly developed Graded Index Perfluorinated POF (GI-PF-POF) and two types of SOFs were evaluated in a three-point macrobending test bed using a laser light source. A systematic experimental design was executed to evaluate the optical fibres’ signal loss as a result of the bending radius, bending deflection and wrap angle of optical fibre around the middle rod of the test bed. The results showed that POF provides higher signal sensitivity and greater robustness against signal attenuation under bending when compared to SOF. The work also unveiled the bending radius of optical fibres at which minimum or no signal loss occurred. This finding is essential for designing embedded optical fibre sensors with high sensitivity.