Investigation of the effect of MWCNT filled epoxy adhesives in enhancing the quality of dissimilar material bonded joints

Abstract

Achieving a high quality adhesive bond between any two parts (also called adherends) requires the presence of a strong adhesive and a strong adhesive/adherend interface, which are both capable of sustaining the stresses that arise within the bonded joint during its service life. The objective of this study is to improve the bond of metal-to-composite joints by modification of the adhesive properties and the adhesive/adherend interface through the addition of multi-wall carbon nanotubes (MWCNTs). MWCNT/epoxy composites of various weight fractions, i.e. 0.1, 0.3, 0.5 and 1% were manufactured and characterised via a series of mechanical tests in order to assess the effect of different dispersion methods and CNT loadings. Once the mechanical properties were optimised, the MWCNT reinforced epoxy was utilised for the manufacturing of metal-to-metal and metal-to-composite adhesively bonded joints. Co-cured carbon fibre reinforced laminate to steel (CFRP/Steel), glass fibre reinforced laminate to steel (GFRP/Steel) and glass fibre reinforced laminate to aluminium (GFRP/Aluminium) single lap joints with three overlap lengths, namely 25, 40 and 60 mm, were tested in order to investigate how the MWCNT reinforced epoxy adhesive in relation to the overlap length variation affected the joint performance. Finite element analysis (FEA) was employed to determine the stress field along the overlap length of all dissimilar material joints. The resistance to crack propagation with respect to the different weight fractions of the MWCNT epoxy adhesive was also evaluated via the Mode-I fracture toughness test. Virtual crack closure technique (VCCT) simulation was finally used for the calculation of the critical strain energy release rate. Lap shear strength is found to increase up to 40% when MWCNTS are incorporated into the epoxy adhesive used to bond the two substrates. The utilisation of the MWCNT reinforced epoxy adhesive is also proved to be beneficial for the critical strain energy release rate. The latter increases with the increase of the CNT loading, yielding the highest values for the case of GFRP/Aluminium joints. The results suggest that the addition of MWCNTs enhances the interfacial properties of the joints resulting in the improvement of the joint strength and adhesive fracture energy.