Adhesive contact mechanics of bio-inspired pillars: exploring hysteresis and detachment modes

TL;DR

This paper presents a new model for bio-inspired adhesive pillars that captures the entire approach and retraction cycle, revealing complex detachment modes and hysteresis effects influenced by pillar geometry and interfacial defects.

Contribution

It introduces a model based on Lennard-Jones forces that considers full cycle dynamics, including multiple detachment modes and hysteresis, unlike previous models assuming perfect bonding.

Findings

Detachment involves multiple modes such as crack propagation and decohesion.

Hysteretic losses occur during approach-retraction cycles.

Pillar geometry and interfacial defects significantly influence adhesion behavior.

Abstract

Engineering technologies frequently draw inspiration from nature, as exemplified in bio-inspired adhesive surfaces. These surfaces present textures adorned by pillars, mimicking the topography found on the pads of certain animals renowned for their exceptional adhesive capabilities. The adhesive response is strongly influenced by the morphology of these pillars. In typical existing models, perfect bonding conditions are assumed between the pillar and the countersurface, and solely the detachment process of the pillar from the countersurface is investigated. The proposed model, based on the assumption that interactions at the interface are governed by van der Waals forces modeled by the Lennard-Jones potential law, enables the examination of the entire approach and retraction cycle, tracking the movement of the pillar towards and away from the countersurface. Our findings reveal that adhesive contact mechanics is primarily influenced by the geometry of the pillar and the potential presence of interfacial 'defects', which in turn affect the distribution of contact pressure. Furthermore, we show that the detachment process may simultaneously involve various modes of separation, such as crack propagation from outer edge, crack propagation from inner defects, and uniform decohesion. This suggests that existing theoretical models alone cannot fully elucidate the complexity of detachment phenomena. Additionally, we anticipate the occurrence of hysteretic losses during the approach-retraction cycle, attributed to pull-in and pull-off contact jumps. Adhesive hysteresis is a phenomenon consistently observed in experiments but frequently overlooked in existing models.