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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 the mechanical properties of liquid crystal polymer fibres and their adhesion to epoxy resin using laser Raman spectroscopy.

Author: VLATTAS, Cosmas

Year: 1995

Supervisor(s): Costas Galiotis

A number of high performance fibres (aramid, PBZT and PBO) spun from liquid crystal polymer solutions were examined in this work. In particular, a thorough investigation of the mechanical response of these fibres under tensile and compressive deformations was carried out. The major experimental tool employed was the technique of Laser Raman Spectroscopy. It was found that stress-induced changes of these fibres at molecular level are proportional to the macroscopic deformation applied. This correlation is unique for the fibres. A method for converting spectroscopic data to predicted stress-strain curves in tension and compression was proposed. An estimation of their compressive strength was derived and an understanding of the nature of their compressive failure was discussed.
The adhesion of these fibres to epoxy resin was also investigated by monitoring in situ the interfacial stresses developed along the interface/interphase of model single fibre composite coupons. The strength of the interfacial bond was measured. The effect of various parameters such as fibre modulus, fibre diameter and fibre nature upon the interfacial strength of the various systems was evaluated. The mechanisms of stress transfer along with the nature of interfacial damage was examined accurately. It was found that the major parameter controlling the above mechanisms was interfacial yielding in shear. A numerical approximation (using Finite Element Analysis) was employed in order to evaluate the experimental results. Finally, general conclusions concerning the performance of these fibres were drawn. (DXN005121)