No abstract

This paper reports the characterisation methods used in evaluating the chemical changes in glass fibre/epoxy prepregs during storage in an environment chamber. The specimens were exposed to an environment with a relative humidity of 50% at 25°C for up to 196 days. Various physicochemical analysis methods were used to determine the extent of the changes to the prepregs during storage. These methods include infrared spectroscopy (IR), thermal analysis (TA) and other chemical methods to measure the volatile and insoluble components content. During storage, the chemical reaction occurs between some epoxide groups, which is known as precuring. Results indicate that precuring in the epoxy resin system consumed a considerable number of epoxide groups during the exposure. The epoxide index obtained from IR analysis gives a straight measure of the number of epoxide groups remaining in the prepregs at different stages of the storage. A parameter known as the “precured degree”, defined from the epoxide index, can be used to measure the prepregs’ quality. A set of laminates made from prepregs that had been degraded to different degrees were subjected to flexural and tensile testing. The flexural and tensile properties were significantly reduced as a consequence of the increase in the precured degree for the prepregs. The results show that it is important to control the precuring reaction in epoxy-based prepregs during storage before they are transferred into composite products.

No abstract

No abstract

This paper investigates the influence of hydrogen loading and other stages of the fabrication process on the mechanical strength of fibre Bragg gratings. Following UV-irradiation, tensile tests were carried out on Ge-B codoped photosensitive fibres with and without hydrogen loading. Fibre Bragg gratings (FBGs) were written using a range of UV wavelengths, namely 246 nm, 255 nm and 266 nm. The tensile strength of the optical fibres was determined in their as-received status and following the various stages of FBG fabrication. The mechanical strength was assessed using Weibull statistics. The results indicate that the strength of FBGs is influenced by the UV irradiation parameters and by the hydrogen-loading process. FBGs fabricated using shorter UV wavelengths and low pulse power intensity exhibit a high mechanical strength. The FBGs written in hydrogen loaded fibres have less than 50% of the strength of FBGs that have not been hydrogen-loaded. Fibre fracture morphology observed by scanning electron microscope (SEM) reveals fracture mechanisms of FBGs, which are correlated with the structural change of the silica fibres induced during the FBG