Effect of MWCNT filled epoxy adhesives on the quality of adhesively bonded joints

Most adhesively bonded joints exhibit adhesive or cohesive failure, i.e. failure at the adhesive/adherend interface or within the adhesive, respectively. The main objective of this study is to investigate the effect of surface modification of the metal substrate accompanied by modification of the adhesive properties on the strength and failure mechanism of bonded joints. A 5061 aluminium alloy has been used as the metal substrate onto which two types of surface treatments were applied; chemical surface modification and gritblasting. A standard epoxy resin was used as the adhesive medium, in which multi-wall carbon nanotubes (MWCNTs) were dispersed, with a range of weight fraction content (from 0.03% to 0.5%). The resin was fully characterised by mechanical testing in order to determine the optimum weight fraction to enhance its properties. Aluminium to aluminium and glass fibre reinforced polymer (GFRP) composite to aluminium single lap joints bonded with either pure epoxy resin or MWCNT reinforced epoxy resin were subsequently manufactured and tested. The tests show a moderate increase of the joint strength when MWCNTs are added into the adhesive with the failure mechanism changing from cohesive to adhesive. In addition, the comparison between different surface preparation methods shows that gritblasting results in considerably improved adhesive strength over chemical treatment.