Abstract:
The study reported in this thesis investigates the relationships between the
morphology of PEI/epoxy blends reinforced with glass fibres and their fracture
properties.
Hot stage optical microscopy is used to study the phenomenon of phase
separation in the thermosetting blends in the presence of glass, carbon and
aramid fibres. Phase separation is shown to be unaffected by the presence of
aramid and carbon fibres, but is affected by the presence of glass fibres, to a
degree which mainly depends on the PEI concentration. Other parameters like
cure temperature, the nature of the glass fibre surface and fibre volume fraction
are also examined. The most striking feature is the initiation and development
of an epoxy-rich layer around the fibres for blends modified with 15 wt % PEI.
This concentration corresponds to a co-continuous network of PEI-rich particles
embedded in an epoxy-rich matrix.
The effects of morphologies formed during phase separation on the
fracture properties of glass fibre-reinforced composites are studied using the
mixed-mode bending test rig developed by NASA. Extensive scanning electron
microscopy (SEM) observations provide qualitative support to the delamination
results. They show that different micro-mechanisms of deformation can occur,
depending on the matrix microstructure and the fibre/matrix interfacial strength.
SEM observations show that cusps are not only present under mode II
loading, but also under mixed-mode I/II loading. They reveal that the spatial
density and angle of cusps depend on the applied loading mode, the interfacial
strength and the nature of the matrix itself. These observations are the base of
a model which describes the delamination behaviour of composites from pure
mode Ito pure mode II loading.
