| Summary: | Effective, non-destructive and in-situ damage detection in fibre reinforced composites (FRCs) is a field of great research interest worldwide. Currently employed optical fibre based sensors suffer from diameter mismatch between optical fibres and the reinforcing fibres, stress-transfer issues, bonding problems, temperature sensitivity and are mostly complex. Therefore the aims of this project were to investigate the use of E-glass reinforcing fibres for optical transmission and to develop a fully functional, simple and economic but effective, optical health monitoring system for epoxy matrix composites using the reinforcing fibres as the self-sensing element. E-glass fibres have been converted to optical waveguides using a variety of coatings. It has been found that reinforcing fibre could transmit light over a certain range depending on the transmitting wavelength, chemical purity of glass fibres, fibre diameter, quality and in particular the optical properties of the cladding material and fibre/matrix interface which have a strong effect on the numerical aperture. In this work, commercial grade aerospace certified epoxy, Araldite L Y IHY 5052 was employed as the matrix and to ensure that it had suitable optical properties to act as a cladding for light guiding its refracti ve index was lowered by blending with propylene carbonate. The effects of this addition on the mechanical properties of the resin were assessed. Wavelengths at which attenuation was minimised were identified and the corresponding transmitters and detectors were acquired to build a complete optical measurement setup. A variety of composite test panels were constructed including hybrid glass-carbon fibres. It is shown that the system detects damage including barely visible impact damage (BVID) and can give some indication of stress variation. Overall the system developed is simple, non- destructive, inexpensive to deploy and maintain, easy to operate, suitable for in-situ employment and gives real-time results.
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