Torsional Instabilities in the Delamination of Soft Adhesives

TL;DR

This paper investigates how soft adhesives fail under combined shear and torsion, revealing delamination mechanisms through experiments and a theoretical model, which can inform better adhesive design.

Contribution

It introduces a novel experimental setup and a theoretical framework to study torsional delamination in soft adhesives, addressing a gap in understanding failure under complex loads.

Findings

Delamination nucleates at imperfections and propagates circumferentially.

Stick-slip behavior observed during delamination process.

Material parameters influence the delamination and sliding behavior.

Abstract

Soft adhesive contacts are ubiquitous in nature and are increasingly used in synthetic systems, such as flexible electronics and soft robots, due to their advantages over traditional joining techniques. While methods to study the failure of adhesives typically apply tensile loads to the adhesive joint, less is known about the performance of soft adhesives under shear and torsion, which may become important in engineering applications. A major challenge that has hindered the characterization of shear/torsion-induced delamination is imposed by the fact that, even after delamination, contact with the substrate is maintained, thus allowing for frictional sliding and re-adhesion. In this work, we address this gap by studying the controlled delamination of soft cylinders under combined compression and torsion. Our experimental observations expose the nucleation of delamination at an imperfection and its propagation along the circumference of the cylinder. The observed sequence of `stick-slip' events and the sensitivity of the delamination process to material parameters are explained by a theoretical model that captures axisymmetric delamination patterns, along with the subsequent frictional sliding and re-adhesion. By opening up an avenue for improved characterization of adhesive failure, our experimental approach and theoretical framework can guide the design of adhesives in future applications.