UBC Theses and Dissertations
Theoretical limits in detachment of fibrillar dry adhesives under geometrical confinement Hoseynian Benvidi, Seyed Farid
Fibrillar dry adhesives are state-of-the-art solutions for controllable and reversible attachments, inspired by nature from animals like the gecko. They depend on short-ranged intermolecular bonds, necessitating discrete attachment terminals with low elastic modulus in order to conform to the adhered material's surface roughness. At the same time, high stiffness grants resistance against interfacial crack growth and detachment under external loading. Nature provides us with a solution to this contentious requirement in the form of bi-material composite adhesives consisting of a soft tip confined by a much stiffer backing, significantly improving the adhesive performance. However, different detachment mechanisms introduced by this design and the adhesive strength corresponding to them have not been thoroughly investigated. We study the adhesive strength of an axisymmetric bi-material with a soft tip adhered to a rigid substrate subjected to normal loading, using linear elastic fracture mechanics. Two major detachment mechanisms are noticed: Crack propagation from the perimeter of the interface and from its center. Geometry and incompressibility of the adhesive layer determine the predominant detachment mode. For a geometrically confined tip under certain conditions, the maximum adhesive strength becomes independent of the crack size due to center crack stable propagation. This maximum adhesive strength is ultimately presented in the form of a power-law equation evidencing an increase in adhesive strength for thinner tips. Finally, we found a good agreement between our results and experiments.
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