Search

The results of a study of environmental ageing on the apparent interfacial shear strength of glass fibre–vinyl ester microbond samples are presented. The scale related issues of estimating water absorption levels in microbond samples are reviewed and discussed and a solution based on Fickian diffusion is given. Interphase strength of microdroplets aged in water at 23°C was relatively stable up to 6 days exposure after which strength degradation was fairly rapid. Immersion in water at 50°C resulted in an immediate 20–30% irreversible loss of strength. Further exposure beyond 2 days led to total loss of integrity of the microbond samples. Electron microscope images of aged microdroplets appeared to show the development of a bi-phasic microstructure. The presence of two phases in small scale vinyl ester polymer samples was confirmed by DMA on thin films. [ABSTRACT FROM AUTHOR]

The work presented focuses on the need to better understand the effect environmental conditions, namely humidity, have on the interfacial shear strength (IFSS) of composites. The IFSS was first characterised using the microbond test method in a laboratory atmosphere. A specialised rig was then designed and manufactured in order to carry out the microbond test in a dynamic mechanical analyser with a humidity chamber accessory. Due to the well-known moisture absorbing nature of polyamide matrices, the effect of a range of conditions from 0 to 90% relative humidity was investigated. Results presented for both methods are based on the use of a Polyamide 6 matrix. Steel fibres are used extensively for method development and comparison throughout this work. Finally, successful testing on the primary system of fully sized HiPer-Tex™ glass fibre polyamide 6 effectively shows that humidity influences the measured apparent IFSS. [ABSTRACT FROM AUTHOR]

A number of analytical techniques were applied to investigate changes to the surface of unsized boron-free E-glass fibres after thermal conditioning at temperatures up to 700 °C. Novel systematic studies were carried out to investigate the fundamental strength loss from thermal conditioning. Surface chemical changes studied using X-ray photoelectron spectroscopy (XPS) showed a consistent increase in the surface concentration of calcium with increasing conditioning temperature, although this did not correlate well with a loss of fibre strength. Scanning electron microscopy fractography confirmed the difficulty of analysing failure-inducing flaws on individual fibre fracture surfaces. Analysis by atomic force microscopy (AFM) did not reveal any likely surface cracks or flaws of significant dimensions to cause failure: the observation of cracks before fibre fracture may not be possible when using this technique. Fibre surface roughness increased over the whole range of the conditioning temperatures investigated. Although surface roughness did not correlate precisely with fibre strength, there was a clear inverse relationship at temperatures exceeding 400 °C. The interpretation of the surface topography that formed between 400–700 °C produced evidence that the initial stage of phase separation by spinodal decomposition may have occurred at the fibre surface. [ABSTRACT FROM AUTHOR]