A new study published in Engineering presents a significant advancement in dry adhesive technology. Researchers from Xi'an Jiaotong University, including Duorui Wang, Hongmiao Tian, Jinyou Shao, and others, have developed a self-adaptive core-shell dry adhesive with a "live core" that shows remarkable performance in high-strength adhesion under non-parallel contact.
Gecko-inspired van der Waals force-based adhesion technology has great potential in robotic operations. However, non-parallel contact, which is common in engineering applications, often weakens the adhesion and reduces the stability and efficiency of tasks. In the past, artificial dry adhesives with high-theoretical adhesion values failed to perform well in practical use due to non-parallel contact issues.
The newly proposed adhesive is inspired by the soft muscle and rigid bone in a gecko's sole. It consists of a top adhesion tip with a mushroom-like geometry for interfacial adhesion based on van der Waals forces and a bottom core-shell configuration for interface stress regulation. Different from traditional core-shell structures with a fixed "dead core," the "live core" in this new adhesive can rotate within the soft shell, similar to skeletal joints. This rotation enables stress equalization at the interface and helps the adhesive adapt to macroscopic interfacial angle errors.
The researchers fabricated the adhesive using materials like polydimethylsiloxane (PDMS) and silicone rubber. They characterized the microstructure and mechanical properties of the adhesives and tested their adhesion performance under both aligned and misaligned conditions. The self-adaptive core-shell adhesives show an adhesion strength 100 times higher than conventional homogeneous structures under non-parallel contact. They also have anti-overturning ability, which is crucial for stable grasping in robotic operations.
Finite element analysis (FEA) was used to reveal the adhesion mechanism. The FEA model showed that the rotation of the rigid piece in the core-shell adhesive effectively reduces the actual misalignment angle and improves the stress distribution at the interface, leading to enhanced adhesion.
The adhesion performance of the new adhesive was quantitatively characterized. It was found that the core-shell adhesives have superior adhesion performance under different preloads, and their adhesion strength remains stable even at high temperatures and in water-rich environments. The researchers also optimized the structure of the adhesive, exploring the influence of factors such as the stiffness of the soft shell and rigid core, the geometric position of the rigid core, and the size of the rigid core on the rotation angle and adhesion strength.
This innovative self-adaptive core-shell dry adhesive has considerable application potential in object manipulation, especially for surfaces with sloping features. It can be used in optical component assembly, where its adaptability to non-parallel contact and anti-overturning ability are highly valued. Overall, this new adhesive technology could advance the development of gecko-inspired adhesion-based devices and systems.
The paper "Self-Adaptive Core-Shell Dry Adhesive with a 'Live Core' for High-Strength Adhesion under Non-Parallel Contact," authored by Duorui Wang, Hongmiao Tian, Jinyu Zhang, Haoran Liu, Xiangming Li, Chunhui Wang, Xiaoliang Chen, Jinyou Shao. Full text of the open access paper: https://doi.org/10.1016/j.eng.2024.12.035 .
