In the current work the microstructure and fracture performance of carbon-fibre reinforced
polymer (CFRP) composites based upon matrices of an anhydride-cured epoxy-resin (formulated
with a reactive diluent), and containing silica nanoparticles and/or polysiloxane core-shell
rubber (CSR) nanoparticles, were investigated. Double cantilever beam tests were performed in
order to determine the interlaminar fracture energy of the CFRP composites, while the single
edge-notched bend (SENB) specimen was employed to evaluate the fracture energy of the bulk
polymers. The fracture energy of the bulk epoxy polymers increased from 173 J/m2 for the
unmodified polymer to a maximum of 1,237 J/m2 with the addition of 16 wt% of CSR
nanoparticles. The toughening mechanisms were identified as (a) localised plastic shear yielding
and (b) cavitation of the CSR particles followed by plastic void growth of the matrix. The steadystate
propagation value of the interlaminar fracture energy of the CFRP composites increased
with increasing nanoparticle concentration, from 1,246 J/m2 for the unmodified epoxy matrix to
a maximum of 1,851 J/m2 with 4 wt% of silica nanoparticles and 8 wt% of CSR nanoparticles.
Crack growth in the CFRP composites was dominated by fibre-bridging toughening mechanisms.
The efficiency of the transfer of toughness from the bulk polymers to the carbon fibre composites
was considered. The measured fracture energy of both bulk and composite materials decreased
at a test temperature of -80°C, compared with room temperature, i.e. 20°C. Nevertheless, the
toughening effects of both the silica and CSR nanoparticles on the bulk epoxy polymers and the
CFRP composites, compared with the unmodified epoxy polymers, were still evident even at the
lower temperature. Indeed, the toughening effect of the silica nanoparticles was greater at -80°C
than at room temperature.