# Investigating the normal and tangential peeling behaviour of gecko spatulae using a coupled adhesion-friction model

## TL;DR

This study uses a coupled adhesion-friction model to analyze gecko spatula peeling behavior, revealing how design parameters influence attachment strength and detachment ease, with implications for bio-inspired adhesive systems.

## Contribution

It introduces a nonlinear finite element model that explains gecko spatula adhesion and detachment mechanisms, considering various parameters affecting pull-off forces.

## Key findings

- Partial sliding increases peel force during tangential peeling.
- Spatula pad thickness beyond a point does not significantly boost attachment.
- Spatulae detach by changing shaft angle and peeling vertically.

## Abstract

The present work investigates the normal and tangential peeling behaviour of a gecko spatula using a coupled adhesion-friction model. The objective is to explain the strong attachment and easy detachment behaviour of the spatulae as well as to understand the principles behind their optimum design. Using nonlinear finite element computations, it is shown that during tangentially-constrained peeling the partial sliding of the spatula pad near the peeling front stretches the spatula, thus increasing the strain energy and leading to high pull-off forces. The model is used to investigate the influence of various parameters on the pull-off forces -- such as the peeling angle, spatula shaft angle, strip thickness, and material stiffness. The model shows that increasing the spatula pad thickness beyond a certain level does not lead to a significant increase in the attachment forces. Further, the easy detachment behaviour of geckos is studied under tangentially-free peeling conditions. It is found that the spatulae readily detach from the substrate by changing their shaft angle and eventually peel vertically like a tape. Since the present computational model is not limited by the geometrical, kinematical, and material restrictions of theoretical models, it can be employed to analyse similar biological adhesive systems.