Experimental and numerical analysis on the cohesive behavior of an automotive adhesive improved by MWCNT subjected to mode I and II loadings

This paper presents the effect of multi-walled carbon nanotubes (MWCNT) incorporation in the fracture and damage behavior of an epoxy adhesive. In this regard, the fracture energies and cohesive behavior of the neat and reinforced adhesives are obtained by testing Double Cantilever Beam (DCB) and End-Notched Flexure (ENF) specimens in mode I and mode II, respectively. The cohesive behavior is studied by extracting traction-separation law (TSL) corresponding to each and every adhesive using direct method. In order to validate the extracted TSL, an experimental test and numerical simulation on Single Lap Joint (SLJ) specimens are conducted. The good agreement between experimental and numerical load-displacement responses proves the accuracy and precision of TSLs. The results revealed that in pure modes, the fracture toughness of the epoxy adhesive is improved by adding MWCNTs up to a critical %wt. Afterwards, incorporating excess additive would weaken the adhesive. Similarly, load-displacement responses of SLJs indicates that the highest improvement of the joint energy would be achieved using the same critical %wt and result in an enhancement of over 80%.