Pull-off strength of mushroom-shaped fibrils adhered to rigid substrates

TL;DR

This study uses a computational model to analyze the detachment behavior of mushroom-shaped fibrils, revealing how geometry and defects influence their adhesion strength and stability, aiding the design of improved bio-inspired adhesives.

Contribution

It introduces a cohesive zone model-based analysis of mushroom-shaped fibril detachment, highlighting the effects of geometry and defects on adhesion performance.

Findings

Wider, thinner caps reduce stress concentrations.

Central detachment is promoted by specific geometries.

Adhesion defects significantly lower pull-off strength.

Abstract

The exceptional adhesion properties of biological fibrillar structures -- such as those found in geckos -- have inspired the development of synthetic adhesive surfaces. Among these, mushroom-shaped fibrils have demonstrated superior pull-off strength compared to other geometries. In this study, we employ a computational approach based on a Dugdale cohesive zone model to analyze the detachment behavior of these fibrils when adhered to a rigid substrate. The results provide complete pull-off curves, revealing that the separation process is inherently unstable under load control, regardless of whether detachment initiates at the fibril edge or center. Our findings show that fibrils with a wide, thin mushroom cap effectively reduce stress concentrations and promote central detachment, leading to enhanced adhesion. However, detachment from the center is not observed in all geometries, whereas edge detachment can occur under certain conditions in all cases. Additionally, we investigate the impact of adhesion defects at the fibril center, showing that they can significantly reduce pull-off strength, particularly at high values of the dimensionless parameter \c{hi}. These insights contribute to the optimization of bio-inspired adhesives and microstructured surfaces for various engineering applications.