Discontinuities at the interface and adhesion

An adhesive bond does not necessarily fail at its oweakest linko. The loading mode, the thickness of the adherends and adhesive layer, the presence of localised flaws, and the residual stress state within the adhesive layer can all affect the failure strength and energy of an adhesive bond. This means that very similar adhesive bonds may exhibit different failure energies and different loci of failure. This paper reviews some examples from the literature where the introduction of discontinuities at the interface also leads to differences in failure energy and locus of failure. The influence in this way of microporous and microfibrous surface features in anthropogenic adhesive bonds are well-established. More recently, it has been recognised that analogous effects occur in some examples of adhesion in the natural world. The remarkable climbing ability of the gecko depends of a fine state of subdivision at the interface between the animal's foot and the substrate. Studies of natural adhesion have stimulated the development of biominetic adhesive systems, for example using photoresist technology to produce microfibrous and microporous surfaces.