Application of functionally graded adhesives in aluminium-composite joints

Abstract

Adhesive joints are characterized by non-uniform distribution of stresses and strains along the bond-lines, with maximum values near the ends of the overlaps. This phenomenon can cause the premature failure of the joints, being specially critical when brittle or semi-brittle structural adhesives are considered. This has motivated the research in the field of ‘functionally graded adhesive’ (FGA) or ‘multiple-adhesive’ joints, which reduce the phenomena described through a combination of rigid and brittle adhesives with more flexible and ductile ones. In this way, these strategies allow to notably increase the joints maximum load capacity. In this field, this article presents the work carried out by ITAINNOVA within the project SAFEJOINT. Specifically, the potential of the techniques based on ‘banded’ gradings as approximations of the continuum gradings is analysed. The study is focused in aluminium-composite single lap shear (SLS) joints with epoxy adhesives. The work done covers both the numerical optimisation of the joints and the fabrication and testing of samples in order to verify experimentally the potential for improvement of the technique comparing with mono-adhesive joints. Finally, an example of application of the technology is presented.

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