The effect of geometry on the adhesive behavior of bio-inspired fibrils

Inspired by the special climbing ability of geckos and insects, the effects of geometry, including the end-shape and size, on the adhesion features of bio-inspired fibrils, are investigated. It is found that, the adhesion force of a mushroom-shaped fibril in perfect contact with a rigid substrate decreases with the increase of the peeling angle, but it will increase with an increasing flange thickness at a determined peeling angle. With the same contact length, the mushroom-shaped fibril can achieve much larger adhesion forces than the cylindrical or spatular one due to a larger effective region of the cohesive zone. The effect of the shaft width of the mushroomed-shaped fibril on the adhesion force with and without interfacial defects is also considered, and the results are further compared qualitatively with the experimental ones. A critical contact length for the mushroom-shaped fibril is further found, above which the adhesion force attains a maximum. For a multi-fibril structure, the phenomenon of almost equal load sharing for each fibril is verified numerically, which is consistent with the existing experimental observation. All the results in this paper should be helpful for the understanding of the micro-adhesion mechanism of biological adhesive systems and the design of novel adhesives.