Fracture behaviours of nano-silica modified epoxies at elevated temperatures

An experimental investigation was conducted to characterize the mechanical properties of nano-silica modified epoxies at room temperature and elevated temperatures. A commercial nano-silica dispersed epoxy product was used as modifiers to toughen a DGEBA epoxy resin. Fracture toughness and other material properties of the cured epoxies were measured using the standard compact tension (CT), tensile and flexural test methods to investigate the effects of the nano-silica on fracture behaviours of the cured epoxies at 23°C, 50°C and 70°C. It has been found that the fracture toughness of the nano-silica modified epoxies have been significantly increased at 23°C and 50°C, while the strength and modulus of the materials remain unchanged or slightly higher. The increases in KIC at room temperature and 50°C are up to 50% and 70% respectively, compared to the unmodified epoxies. At 70°C, the effect of nano-silica on the fracture behaviour diminished because of the change of failure mechanisms from the brittle fracture to the plastic deformation. It is also very encouraging that the nano-silica modified epoxies did not show reduction in glass transition temperature (Tg).