The Effect of Outer Diameter of Multi-Walled Carbon Nanotubes on Fracture Behavior of Epoxy Adhesives

In this paper, the influence of the outer diameter of multi-walled carbon nanotubes (MWCNTs) on the fracture behavior of epoxy adhesives was investigated experimentally and numerically. MWCNTs with three different outer diameters of less than 8, 20-30 and 50-80 nm were used to toughen the epoxy adhesive. Double Cantilever Beam specimens were tested to determine the fracture energy. The results indicated that improvement in the adhesive fracture resistance by introducing MWCNTs was considerably dependent on the outer diameter of MWCNTs. Toughening the epoxy adhesive by incorporating MWCNTs with 8 nm diameter improved the adhesive fracture energy three times higher compared to the MWCNTs with larger diameters. The SEM fractography of the fracture surfaces was also utilized to assess the governing fracture mechanisms occurred in the toughened epoxy adhesives. Moreover, a cohesive zone model was used for numerical investigation of the effect of the MWCNT diameter on the damage behavior of epoxy adhesives.