Nanoindentation, compression and fractural characterization of highly dispersed epoxy silica nanocomposites

Uniaxial compression tests were conducted in this study in order to investigate the compressive properties of the unmodified and nanomodified epoxy with silica nanoparticles. An instrumented nanoindentation technique was also used to investigate its applicability for measuring mechanical properties for such nanocomposite systems. Additionally, the fracture toughness of the unmodified and nanomodified epoxy was measured with single-edge-notch bending tests. The Young's modulus was found to significantly improve with addition of silica nanoparticles and increase with increasing filler content when measured with both compression and nanoindentation tests. The modulus obtained from the nanoindentation testing was 4-8% higher than the one obtained from the compression tests. As expected, the addition of silica nanoparticles had a significant impact on the fracture toughness and fracture energy and increased with increasing filler content, while observation of the fracture surfaces using SEM suggested that the nanoparticles affected the fracture behavior of such epoxy systems. Implementation of an analytical model in the current nanomodified epoxy network as compared with the experimental fracture energy results showed that the 15% matrix void growth, from debonded nanoparticles, as well as the matrix shear banding are the governing mechanisms of energy absorption.