Damage detection in composites using e-glass fibre and small diameter optical fibre

The primary aim of this study was to demonstrate that E-glass and custom-made small diameter optical fibres, with an outer diameter of 12 micrometres, can be used to monitor the following: (i) In-situ monitoring of the partial dissolution of the cladding on the small-diameter optical fibres in hydrofluoric acid. This was necessary for the small-diameter optical fibres as the thickness of the original cladding was not appropriate to enable evanescent wave spectroscopy. (ii) In-situ monitoring of the impregnation process. Since the cladding was etched to access the evanescent field in the optical fibres, it was demonstrated that the impregnation of the fibres by the resin could be monitored. (iii) In-situ cure monitoring. After impregnation, the cross-linking reactions taking place at the surface of the glass fibres were monitored using near-infrared spectroscopy. The feasibility of using the glass fibres for monitoring temperature was also demonstrated. (iv) Finally, after the composite was cured, it was tensile tested to failure whilst monitoring the transmitted light intensity through the optical fibres. The un-impregnated bundles were also tensile tested to failure. The failure of the individual filament in the bundle (un-impregnated) and composites were monitored by tracking the intensity of the transmitted light through each filament. Conventional acoustic emission was used to cross-correlate the fracture of the individual filaments. Conventional E-glass fibres can be used as light guides if the conditions for total internal reflection is enabled. In this current study, the matrix served as the cladding. This study has developed a range of techniques that can potentially facilitate the full life cycle monitoring of glass fibre composites. In other words, the same test specimen can be used to monitoring the surface treatment, temperature during drying or heat treatment, cross-linking kinetics and damage during mechanical loading. The self-sensing technique developed in this study can also be used as a tool to study the degradation of properties when the fibres are recycled and reused

Effect of surface treatment and recycling on the mechanical properties of e-glass

The primary focus of this study was to investigate the effect of removing the binder, by specified method, on the tensile strength of E-glass fibre bundle and composites. The methods investigated for removing the binder from E-glass fibres were: (i) fibre spreading; (ii) acetone-based treatment; and (iii) heat treatment in air and in a vacuum. In the first phase of the research, the effect of the above mentioned binder removal methods were investigated using the single-bundle tensile test. Binder removal via fibre spreading did not cause any reduction in the properties of E-glass fibre bundles. However, binder removal by acetone extraction led to a decrease of 37% in the tensile strength. The most detrimental effect on the tensile strength was found to be when E-glass was exposed to temperatures in excess of 450 °C. The percentage reduction in tensile strength for E-glass fibre bundle for 450 °C, 550 °C and 650 °C were 60%, 66% and 90% respectively. In the second phase of the research, E-glass bundles that were subjected to the above-mentioned treatments were used to fabricate single bundle composites. The procedure for manufacturing these composites was developed. It was established that the reduction in the strengths of the E-glass composites after specified treatment could be correlated to the reduction in properties experience by the fibre bundles. Attempts were made to analyse the treated fibres using a range of analytical techniques such as X-ray diffraction, thermographic analysis, differential scanning calorimetry and infrared spectroscopy analysis. Heat treating E-glass fibres in the absence of air was shown to bring about a reduction in the tensile strength by 58% as compared to 78% when the fibres were previously heated in air at 650 °C