Investigation of the strength loss of heat treated glass fibre

Student thesis: Doctoral Thesis


Mechanical reinforcement glass fibre has been shown to demonstrate significant loss of tensile strength following exposure to elevated temperatures; for example when heat treatment is performed, or due to thermal recycling. Numerous previous studies have confirmed this phenomenon and, while some have attempted to explain possible mechanisms of strength loss, a complete understanding has not yet been presented in the literature.In the work presented in this thesis the phenomenon of strength loss due to heat treatment was investigated using boron-free E-glass fibres, which were coated with either γ-aminopropyltriethoxysilane (γ-APS) or had no surface coating applied during manufacture (unsized/bare). Novel methods of heat treatment were developed and techniques including tensile testing and various thermal analyses were employed. The fibre surface was investigated by X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray spectroscopy (SEM-EDX).By application of a single fibre heat treatment approach it was found that the retained fibre tensile strength after conditioning can be underestimated when using the standard method of heat treating fibre bundles. Strength loss may be comprised of two components: the first component, mechanical handling damage, was carefully controlled using the single fibre heat treatment approach, but is also minimised by presence of sufficient surface γ-APS coating.The second component is the fundamental strength loss due to thermal effects, which was found to be most critical in the temperature range 450 - 600 °C.The effect of water during heat treatment of unsized fibre was studied using a Thermal Volatilisation Analyser (TVA) in which simultaneous application of vacuum and elevated temperature is possible. It was found that single fibres conditioned using TVA at 450 °C had a strength that was not significantly different from that of fibres that were conditioned similarly but in a standard air furnace.Surface chemical changes of heat treated fibres were investigated. Results of XPS analysis suggested that the surface concentration of calcium increased with increasing conditioning temperature up to 600 °C. Results obtained using Energy Dispersive X-ray spectroscopy (SEM-EDX) showed an increase in the concentration of potassium in the near surface region when fibres were heat treated in excess of 600 up to 700 °C. Significant physical changes at the fibre surface were also observed following heat treatment between 600 - 700 °C. Results of AFM analysis showed that the RMS surface roughness approximately doubled and features became visible by SEM.Across the entire temperature range 200 - 700 °C, over which both roughness and retained fibre strength were investigated, a general trend of increasing surface roughness and decreasing fibre strength was found; however, there was not a correlation between regions of most significant strength loss and large increases in roughness.
Date of Award28 Sep 2016
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorJames Thomason (Supervisor) & James Wood (Supervisor)

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