Results are presented on E-glass fibre properties after thermal conditioning up to 600 °C. Thermal conditioning led to up to 70% strength degradation. Tensile strength and failure strain of silane-coated fibres were relatively stable up to 250 °C but exhibited a precipitous drop at higher conditioning temperatures. Unsized fibres exhibited a linear decrease in strength with increasing conditioning temperature. Little significant strength regeneration was obtained from a range of acid and silane post-treatments of heat conditioned fibres. A simple analysis of the cumulative fibre strength probability resulted in more useful understanding than the Weibull method. The modulus of both fibre types increased linearly with conditioning temperature. Evidence was found of a slow time-dependent reduction of glass fibre modulus during storage in an uncontrolled environment. The results are discussed in terms of the changes in surface coating and bulk glass structure during heat conditioning and the role of the glass fibre water content.

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The properties of glass fibres after conditioning at composite recycling temperatures

The recovery and reuse of glass fibres from manufacturing waste and end-of-life composites in an environmentally-friendly, cost-effective manner is one of the most important challenges facing the thermosetting polymer composites industry A number of processes for recycling fibres from such materials are available or under development However, nearly all options deliver recycled glass fibres that are not cost-performance competitive due to the huge drop in strength of recycled glass fibre compared to its original state A breakthrough in the regeneration of recycled glass fibre performance has the potential to totally transform the economics of recycling such composites This paper reviews the available knowledge of the thermally-induced strength loss in glass fibres, discusses some of the phenomena that are potentially related and presents the status of research into processes to regenerate the strength and value of such weak recycled glass fibres

Glass fibre strength: a review with relation to composite recycling

Direct observation of electron-beam-induced densification and hardening of silica nanoballs by in situ transmission electron microscopy and finite element method simulations

Effects of stress on diffusion of water into silica glass were studied at several temperatures by hydrothermally treating the glass under applied stress. The surface hydrogen concentrations were determined using nuclear reaction analysis and the hydroxyl concentration profiles were analyzed with a Fourier transform infrared spectrophotometer. It was found that the effects of stress on water diffusion into silica glass strongly depend upon temperature; specifically the concentration of water in the glass surface is higher in glass under compression than in glass under tension at low temperatures (e.g., 250°C), while an opposite behavior was observed at high temperatures (e.g., 650°C). On the other hand, the effective diffusion coefficient of water was higher under tension than under compression at low temperatures, while the opposite behavior was observed at higher temperatures. The low temperature behavior was attributed to the effect of stress on the kinetics of water uptake, and the high temperature behavior was attributed to the effect of applied stress on the glass-water reaction equilibrium.

Effect of stress on water diffusion in silica glass at various temperatures

Effects of water on the mechanical properties of silica glass using molecular dynamics

The stress-rate dependency of the mechanical strength of sodium silicate glass with high water content (up to ~25% by weight) was investigated. The glasses were prepared by drying commercial sodium silicate solution in an oven or an autoclave. The mechanical strength of the glasses was measured by a four point bending method at various stress rates. These glasses showed a strong stress rate dependency even in dired paraffin oil and the dependency increased with increasing water content ; the value of n, a measure of the stress rate dependency, was approximately 5 for glasses with ~25 wt% water. At the same time Young's modulus decreased with increasing water, content. It is suggested that stress-induced motion of water is responsible for the increased stress rate dependency. In addition, the apparent value of Young's modulus decreased with decreasing stress rate. This phenomenon was explained in terms of the visco-elastic property of the glasses.

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M. Tomazawa

Papers

Dynamic fatigue of sodium-silicate glasses with high water content