Mode II fracture energy in the adhesive bonding of dissimilar substrates: carbon fibre composite to aluminium joints

Abstract

The end-notched flexure (ENF) test calculates the value of mode II fracture energy in adhesive bonding between the substrates of same nature. Traditional methods of calculating fracture energy in the ENF test are not suitable in cases where the thickness of the adhesive is non-negligible compared with adherent thicknesses. To address this issue, a specific methodology for calculating mode II fracture energy has been proposed in this paper. To illustrate the applicability of the proposed method, the fracture energy was calculated by the ENF test for adhesive bonds between aluminium and a composite material, which considered two different types of adhesive (epoxy and polyurethane) and various surface treatments. The proposed calculation model provides higher values of fracture energy than those obtained from the simplified models that consider the adhesive thickness to be zero, supporting the conclusion that the calculation of mode II fracture energy for adhesives with non-negligible thickness relative to their adherents should be based on mathematical models, such as the method proposed in this paper, that incorporate the influence of this thickness.

Keywords:

• structural adhesives
• aluminium-composite joints
• ENF test
• fracture energy

Acknowledgements

The authors wish to thank Antonio Conesa of Henkel Loctite for providing the adhesives and dispensers needed to perform the tests, as well as the Technical University of Madrid for funding this project (Q105605177).