Direction-dependent adhesion of micro-walls based biomimetic adhesives

The adhesive properties of a biomimetic anisotropic micro-structured surface are investigated. The system is constituted by parallel elastic wall-like structures topped with a thin film. The micro-walls are assumed in perfect contact with a rigid substrate and the adhesive interaction is modeled by considering full contact conditions. Because of its crack trapping behavior, this geometry, when loaded with an external moment acting perpendicularly to the walls direction, shows enhanced adhesive properties compared to the simple flat surface.In the present paper, we study how the adhesive properties depend on the direction of crack propagation. In particular, we determine how the applied moment needed to detach the adhesive depends on the angle that the crack propagation direction makes with the micro-walls one. We find that crack trapping occurs only when crack propagates perpendicularly to the walls. In all the other cases, the system compliance linearly increases with the crack length, causing the energy release rate at the crack to be constant during the crack propagation: crack trapping cannot occur in such conditions.We also propose a simplified analytical model, based on the Euler-Bernoulli beam theory, to calculate the adhesion strength of the system. Analytical solution and numerical calculations show perfect agreement for all directions of crack propagation and values of geometrical parameters