Peeling condition analysis of biomimetic adhesive structure – a finite element study

Gecko and many insects have nanoscale fibrillary structures on their feet serving as adhesive devices. In recent years, van der Waals interaction has been proven to be the primary molecular origin for this kind of phenomena. However, the peeling zone and the cohesive zone both play significant roles in the peeling process while the peeling zone can be described by van der Waals force and the cohesive zone is dependent of molecular interaction. In this reported work, the case of peeling of two elastic bodies, in which the pull-off force depends linearly on the cohesive stress and is independent of the work of adhesion is considered. The adhesion interaction and peeling condition between a single biomimetic adhesive structure and a substrate is simulated as an axisymmetric geometries model, by encoding van der Waals force and molecular interaction in COMSOL software. The simulation takes theoretical fundamental equations as inputs, and by varying relative peel angles, functional variables are built to estimate peeling processes of the biomimetic adhesive structure in various conditions. The results show that the maximum pull-off force of the structure with different materials and pull-off force is decreasing in the peeling process but the cohesive force immediately raises while the contact area becomes smaller. Stress concentration occurs both on the top and at the base of the structure during the peeling process. The simulation results demonstrate that an optimal shape of the adhesive structure can be achieved by examining the simulated pull-off forces. To avoid failure occurring during the peeling process, the structure with a large base can decrease the stress concentrate at the bottom. Based on the analysis, the adhesive structure with an optimised half-hourglass shape is proposed.