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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: A study of carbon fibre epoxy resin interface using Remote Laser Raman Microscopy

Author: PAIPETIS, Alkiviadis

Year: 1997

Supervisor(s): Costas Galiotis

The micromechanics of reinforcement of model carbon fibre / epoxy composites has been investigated using the technique of Remote Laser Raman Microscopy. The technique allows in situ axial stress monitoring in highly crystalline fibres, such as carbon.
For this purpose a remote fibre-optic probe was designed and tested. Tailor-made optics have been introduced at both input and output positions of each fibre-optic to provide laser collimation and maximum efficiency. The probe design takes advantage of the pinhole nature of the optical fibre to achieve depth discrimination.

A full characterisation of the high modulus M40 fibres using conventional testing and Raman Spectroscopy preceded the study of the stress transfer. The study was performed as a function of fibre sizing, coupon geometry and elevated temperature. Model composites were subjected to incremental tensile loading, while the stress in the fibre was monitored at each level of applied strain. The stress transfer regime was studied in the elastic domain using the short fibre coupon test and shear lag approach was employed to model the stress transfer efficiency of the interface through the use of the shear-lag parameter . The study of the long fibre coupon test led to the identification of interfacial failure mechanisms which were also investigated by Scanning Electron Microscopy (SEM). Finally, the stress build-up in the fibre in the presence of energy dissipation mechanisms was modelled, and the stress-transfer efficiency was assessed at different levels of applied composite strain.