The aim of the present work is to investigate the adhesive properties of a biomimetic micro-structured surface with strongly direction-dependent adhesion properties. 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 adhesion. In a previous work of the authors, it is shown that this geometry, when loaded with an external moment acting perpendicularly to the walls direction, enhances the adhesive properties with respect to a simple flat surface as a result of its crack trapping behavior.
In the present paper we investigate what happens when the crack propagates with a generic angle with respect to the walls, in order to determine the variation of the critical conditions for detachment with the direction of the applied moment. Results show that the crack trapping can occur only when the crack propagates perpendicularly to the walls. In all the other cases, the system compliance linearly increases with the crack length. As a result, the energy release rate at the crack tip is constant during the crack propagation and the crack trapping phenomenon cannot occur.