Effect of functionalised and non-functionalised GNPs addition on strength properties of high viscous epoxy adhesive and lap shear joints

This research explores the combinative effects of graphene nanoplatelets (GNPs) addition, functionalisation, and filler concentration on the mechanical behaviour of high viscous structural adhesive (Araldite 2011) and lap shear joints strength. Non-functionalised, carboxylate (COOH) and amine (NH2) functionalised GNPs were mixed in the amounts of 0.25, 0.5, 0.75 and 1 wt% in the host resin by a modified solution mixing technique. Two configurations of lap joints i.e. single lap joint (SLJ) and double lap strap joint (DLSJ) were manufactured using aluminium alloy 5083 adherends. The strength properties of GNPs/epoxy adhesive and lap shear joints were determined by tensile testing. In the case of adhesive, an increase in the value of elastic modulus and tensile strength were observed, accompanied by a decrease in fracture strain. A maximum increase of 13% in the tensile strength and 39% in elastic modulus was observed with the addition of 1 wt% non-functionalised GNP. The lap joints also showed improvement in terms of joint strength with the addition of GNPs. A maximum improvement in failure load of 36% for SLJ and 25% for DLSJ was observed by the inclusion of 0.75 wt% non-functionalised GNP. Optical and Scanning Electron Microscopy (SEM) was utilized for the analysis of fracture surfaces, and the correlation between nano-reinforcement and strengthening mechanisms was critically discussed.