The thermal behaviour of glass fibre investigated by thermomechanical analysis

Abstract

A TMA procedure has been developed with the capability of probing the thermal behaviour of glass fibre. A single glass fibre was successfully mounted into TMA fibre configuration and several thermomechanical programmes were carried out over a wide temperature range from 20°C to 900°C. It was found that measured coefficient of linear thermal expansion (CLTE) of boron-free E-glass fibre remained constant below 300°C and the values had an excellent agreement with that found in the literature. At higher temperatures an abrupt length change in glass transition region allowed for the determination of glass transition temperature (Tg). The results from isothermal measurement showed significant fibre length shrinkage, which was a function of both temperature and time. It follows that there exist two mechanisms, thermal expansion and structural relaxation, which together account for overall thermomechanical responses of glass fibre. The former is related to the decrease of Young’s modulus at elevated temperatures and the latter is considered responsible for the observed increase of room temperature Young’s modulus after thermally conditioning glass fibre at various temperatures

Glass Fibre Strength—A Review with Relation to Composite Recycling

“…Mechanical loss increases and the modulus decreases with increasing water content in glass [89,90]. Interestingly, this would imply that exposure of glass to elevated temperatures could presumably lower the water content and increase the measured modulus (as has been experimentally observed by Yang and Thomason [54]). It has been suggested that water enters into glasses, accelerated by tensile stress and causes swelling, which reduces modulus and strength in a manner similar to the plasticization effect in polymers [88,89].…”

“…Recent results published by Yang and Thomason [54] provided further evidence of this fibre structural relaxation phenomenon by investigation of the thermo-mechanical properties of single boron-free E-glass fibres. Using a thermo-mechanical analyser, fibre length changes were monitored, and in situ measurement of the fibres Young's modulus was performed.…”

“…From the results of Otto [46] and Yang and Thomason [54], it is quite clear that thermal compaction of GF occurs when they are heated above approximately 300˝C, and this effect correlated with a corresponding increase in the room temperature Young's modulus of the fibre. The temperature range over which this phenomenon acts corresponds closely with that over which enthalpy relaxation of GF by DSC has been shown in numerous works [32,[50][51][52][53].…”

“…There is, however, a separate discussion regarding the axial anisotropy imparted to GF due to straining during the fibre drawing process [54], which results in optical birefringence. In many of the studies that have reported measurements of the birefringence of GF, experiments were also conducted to analyse the effect of heat treatment [32,49,50,55].…”

Strength of Glass and Glass Fibers

“…The linear composition models cannot account for the structural variations or speciation of the network formers, such as SiO2, B2O3, and Al2O3. Secondly, glass density or molar volume is affected by fictive temperature or thermal history of the samples in terms of glass structure relaxation [42][43][44]. In turn, annealed glass has lower fictive temperature, higher density, and hence, higher Young's modulus as compared to the quenched form of the same glass composition.…”