Effect of nanoalumina in epoxy adhesive on lap shear strength and fracture toughness of aluminium joints

Lap shear strength and opening mode fracture toughness of epoxy/alumina nanocomposite adhesives in bonded aluminium alloy joints were determined using a single lap joint, and double cantilever beam and contoured double cantilever beam joints, respectively. Epoxy/alumina nanocomposite adhesives were prepared with 0.5, 1.0, 1.5 and 2.0 wt.% of alumina nanospheres (diameter 23-47 nm) and alumina nanorods (diameter in the range of 10 nm and length less than 50 nm). A significant improvement in the lap shear strength and fracture toughness of nanocomposite adhesives was observed over that of neat epoxy adhesive. Maximum lap shear strength of joints bonded with nanocomposite adhesives was observed at 1.5 wt.% of nanospheres and at 1.0 wt.% of nanorods. Maximum fracture toughness of both types of joint was observed for adhesive having 1.5 wt.% of nanospheres and for 1.0 wt.% of nanorods. However, the fracture toughness of joints having 1.5 wt.% of nanospheres was higher in comparison to the fracture toughness of joints having 1.0 wt.% of nanorods. Lap shear strength and fracture toughness decreased on further increment in the wt.% of nanoalumina i.e. at 2.0 wt.% of nanospheres and, at 1.5 and 2.0 wt.% of nanorods.