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.

中文翻译：

---

使用耦合粘附摩擦模型研究壁虎刮刀的法向和切向剥离行为

目前的工作使用耦合粘附摩擦模型研究壁虎刮刀的法向和切向剥离行为。目的是解释刮刀的牢固附着和易分离行为，并了解其最佳设计背后的原理。使用非线性有限元计算表明，在切向约束剥离过程中，靠近剥离前沿的抹刀垫部分滑动会拉伸抹刀，从而增加应变能并导致高拉脱力。该模型用于研究各种参数对剥离力的影响——例如剥离角度、刮刀轴角度、带材厚度和材料刚度。该模型表明，将抹刀垫厚度增加到超过一定水平不会导致附着力显着增加。此外，在无切线剥离条件下研究了壁虎的易剥离行为。发现刮刀通过改变它们的轴角很容易从基材上分离并最终像胶带一样垂直剥离。由于目前的计算模型不受理论模型的几何、运动和材料限制，因此可用于分析类似的生物粘合剂系统。