Date of Award

5-11-2025

Date Published

June 2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Wanliang Shan

Keywords

Hyperelasticity;Shell Adhesion;Tunable Adhesion;Universal Manipulation

Subject Categories

Engineering | Mechanical Engineering

Abstract

This dissertation investigates the adhesion mechanics of hyperelastic hemispherical shells with finite thicknesses undergoing large deformation against rigid planar substrates. By integrating theoretical modeling, numerical simulations, and experimental validation, a comprehensive understanding of the adherence-detachment behavior of soft elastomeric shell structures is established. The study also applies these insights to the design of soft robotic grippers based on tunable adhesion. To understand the dry adhesion of a free soft shell against a rigid substrate, first, a graphical-numerical modeling framework based on the energy approach is developed and used to predict shell adhesion with a wide range of surface energy, thickness, and stiffness. Experimental characterization is then conducted using a benchmark elastomer as the shell material and pull-off forces as adhesion strength. Both theoretical and experimental results demonstrate that shell thickness and material compliance significantly influence the pull-off force, which means shell adhesion deviates from classical JKR predictions for hemispheres. Specifically, shells with thickness ratios h/R<0.1 exhibit pull-off forces nearly 50% lower when compared to that of a JKR hemisphere. The dissertation further explores the design of soft grippers using hemispherical shells with tunable adhesion triggered by pneumatic actuation. It is found that a soft shell in contact with a rigid substrate under depressurization exhibits much higher adhesion than that of the same shell under zero pressure. This discovery enables robotic pick-and-place operations using soft shells. Through a combination of theoretical and computational modeling efforts and experiments, the underlying mechanism for the observed enhanced adhesion is identified as a combination of dry adhesion and suction. Experiments show that the soft shell grippers exhibit high tolerance to misalignment, while in contrast, adhesion of solid and hollow pillars suffer from misalignment. In addition, through manipulation of how the negative pressure is applied during initiation of adhesive contact, very low preloads for gripping are needed for these soft shell grippers, which makes them suitable for manipulating fragile and lightweight objects. It is demonstrated that the shell grippers can be used to manipulate various objects, regardless of whether they are curved or flat, smooth or rough, wet or dry, soft or rigid, with through holes or not. Shell grippers thus are a very promising platform towards universal manipulation.

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Open Access

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