Advanced composite materials based mainly on epoxy resins are being
used in increasing numbers of components in the aerospace industry.
Such components have to survive in a range of moisture and temperature
environments in different parts of the world at varying altitudes. It
is important therefore to have sufficient information about the behaviour
of composite components to predict what effect these environments
will have on their properties. The aim of the work reported in
this thesis was to provide such information not only for epoxy based
systems but to make comparisons with polyester and vinyl ester based
Five glass fibre reinforced resin systems were used. Two vinyl esters,
one polyester, one straight epoxy and one epoxy prepreg mixture. The
effect of immersion in distilled water and exposure to humid air at 60%
and 95% relative humidity was investigated at temperatures ranging from
25°c to 70oc, for periods of sixteen and forty days. During these periods
moisture uptake for both unidirectional and bidirectional materials was
recorded on a daily basis, and variations in glass transition temperature
were determined. At the end of each period the ultimate tensile
stress, tensile modulus, tensile strain to failure, interlaminar shear
strength and interplanar shear strength of each material was determined.
The water absorption results for the vinyl ester resins, polyester and
straight epoxy resin initially showed Fickian diffusion characteristics.
In the epoxy prepreg material a two stage diffusion process was observed.
No equilibrium water absorption plateau was obtained over forty days at
60% relative humidity for any of the materials, at any temperature. All
the mechanical properties dropped under these conditions and this was
shown to be as a result of degradation at the glass-resin interface. At
95% relative humidity the fall in mechanical properties was greater and
not recoverable. Under these conditions plasticization of the matrix had
occurred. All the material samples which were subject to hot water under-
went pronounced degradation. The degradation process was shown to
be due to penetration of water at the glass-resin interface, followed
by attack on the coupling agent and glass fibre surface. This degradation
process was confirmed.by micro-observations of the fracture
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.