Numerical analysis of interfacial stress distributions and adhesion behaviour of fibrillar surfaces

摘要

The climbing abilities of geckos have inspired many researchers to develop reusable, reversible adhesives. The fabrication of such synthetic adhesives has been well investigated. However, a full theoretical description is still lacking. The objective of the thesis is to improve the theoretical understanding of the mechanics of fibrillar adhesion and also to uncover the various factors influencing the adhesion of the compliant fibrils adhered to a rigid surface using finite element analysis. The effect of fibril geometry on the adhesion was examined. Straight punch and mushroom fibrils were examined numerically and it was found that mushroom fibrils show better adhesion compared to straight punch. Mushroom fibrils with higher stalk to cap ratio and smaller flap height show better adhesion when the corner singularity is considered as driving force for delamination. For these fibrils the detachment will begin from centre instead of corner. Some other shapes were also studied by introducing a fillet radius at the corner joining stalk and the cap.We propose a novel composite fibril with a stiff stalk and a softer tip to replicate the benefits shown by mushroom fibrils but with reduced manufacturing complications. The influence of Young’s modulus and tip height were studied along with different interfacial shapes joining the stiff stalk and soft tip. It is found that higher Young’s modulus ratio and smaller soft tip height result in higher adhesion strength. The results support the rational optimization of synthetic micropatterned adhesives.