Fracture toughness of nanomodified-epoxy systems

The effect of nanosilica, multiwalled carbon nanotubes (MWCNT) and montmorillonite (MMT) nanoclay on critical stress intensity factor and critical energy release rate of Epikote 828 epoxy polymer was studied. Fracture toughness tests were conducted on three types of nanocomposites which contain 5-25 wt% nanosilica, 0.5-1 wt% MWCNT and 1-5 wt% MMT nanoclay. The compact tension specimens of 9 mm initial crack length were fabricated and tested in tension. It was found that, the load at crack growth initiation FQ for all nanomodified polymer systems was higher than that of the neat epoxy. Hence, the presence of nanosilica, carbon nanotubes and nanoclay improves the critical stress intensity factor and critical energy release rate of the polymer. For the nanoclay-modified epoxy system, the degree of enhancement depends on the morphology of the nanocomposites. At high nanoclay content (> 3 wt%), a detrimental effect on the fracture toughness was observed. This is due to a weak nanomer/epoxy interfaces in a highly intercalated structure nanocomposite.