HYBRID TOUGHENING OF EPOXY WITH RUBBER AND NANOSILICA PARTICLES: EXPERIMENTS AND MODELLING

The mechanical properties, fracture performance and toughening mechanisms of an anhydride cured epoxy polymer modified by different combinations of preformed core-shell rubber particles (CSR) and nanosilica particles are investigated. Two types of CSR particles, with diameters of 100 nm and 300 nm, are used. The Young's modulus of the epoxy decreased with the increasing weight percentage of CSR particles, but increased with the addition of nanosilica. Both the compressive modulus and yield stress decreased with the increasing CSR particle content; however, the addition of nanosilica led to an increase of the compressive modulus, while the yield stress remained unchanged. The glass transition temperature of the unmodified epoxy was 159 degrees C and this was unchanged by the addition of CSR particles and nanosilica. The fracture energy increased from 78 J/m(2) for the unmodified epoxy to 530 J/m(2) with an addition of 9 wt% of 100 nm diameter CSR particles and to 403 J/m(2) with an addition of 300 nm diameter CSR particles; this was further enhanced by the addition of nanosilica. CSR particle cavitation was identified as one of the toughening micro-mechanisms through field emission gun scanning electron microscopy (FEG-SEM). The toughening mechanisms of particle-modified epoxies were also investigated through non-linear finite element analyses. The model represents a two-dimensional axisymmetric unit-cell of nanosilica-embedded epoxy under triaxial loading, considering an elastic-plastic response for the epoxy and cohesive interaction between the nanosilica and the epoxy matrix. The model predicts that there is significant plastic deformation of the epoxy before it debonds from the nanosilica, and that both plasticity of the matrix and particle debonding contribute significantly to energy dissipation.