Session: 12-29-01: Mechanics of Soft Materials

Paper Number: 150274

150274 - Interplay Between Geometry and Elasticity in Stiff and Soft Patterned Adhesion 

Designing geometric heterogeneity in an architected material plays an important role in overcoming its strength-toughness conflict and combining the best of both. Similarly, introducing effective interfacial patterns as geometric heterogeneity in adhesion between two materials has proven successful in greatly enhancing the adhesion strength or toughness for both stiff and soft materials, without modifying the inherent material property. Compared to relatively stiff patterned adhesives such as gecko-inspired surfaces, where a great effort has been placed on optimizing the contact and reducing stress concentration, soft patterned adhesives usually ensure a conformal contact, but involve large-scale nonlinear deformation and energy dissipation. As a result, despite the recent progress in utilizing interfacial patterning to enhance crack resistance in soft adhesion, the detailed fundamental interplay between the pattern geometry and material property in determining the final adhesion performance has remained largely unclear. This presentation studies such an interplay by conducting a high-throughput finite element simulation of 90-degree peeling of bilayers with pillar-like interfacial patterns. We investigate adherends made of stiff and soft materials while keeping the intrinsic adhesion toughness identical in all cases by the same cohesive layer in the simulation. We identify the key geometric dimensionless parameters of the interfacial pattern. We compute peeling behaviors of patterned bilayers with a large range of varying geometric parameters and elastic moduli. We find that whereas adherend elasticity plays a minor role in determining the peeling strength in non-patterned uniform interfaces, a softer adherend can dramatically enhance the peeling strength in patterned interfaces. We further investigate the competition between the adhesion strengthening by stress delocalization and crack re-nucleation and the adhesion weakening by reduced contact area, due to the presence of interfacial pattern. Based on these phenomena, a theoretical model for the effective adhesion toughness of patterned adhesion is derived from dimensional analysis, encompassing the cohesive layer, energy released, and the mixture of nonlinear stretching and bending in pillars during debonding. The comparison between the effective adhesion toughness and the uniform-interface adhesion toughness gives rise to the fractocohesive length of the adhesion system, which further determines the condition for effective toughening from patterning. Finally, we discuss the generalization of the length scale comparison, as well as their indication for future studies and important applications. These results are hoped to call for more fundamental investigation on the geometry-property relationship in existing and future architected and patterned material systems, as well as provide design principles for their practical load-bearing applications.

Presenting Author: Ruobing Bai Northeastern University

Presenting Author Biography: Ruobing Bai is an assistant professor in the Department of Mechanical and Industrial Engineering at Northeastern University. He received his BS in Theoretical and Applied Mechanics at Peking University in 2012, and PhD in Engineering Sciences at Harvard University in 2018. He was a postdoctoral fellow in the Department of Mechanical and Civil Engineering at California Institute of Technology from 2018 to 2020. He is the recipient of the Chun-Tsung Scholar in Peking University, the Haythornthwaite Research Initiation Award from the Applied Mechanics Division of American Society of Mechanical Engineers (ASME), and the Extreme Mechanics Letters (EML) Young Investigator Award. He currently serves as a member of the Extreme Mechanics Letters (EML) Early Career Advisory Board, Editor of the iMechanica Journal Club, and Editor of the ASME “Mechanics of Soft Materials” technical committee. Research in the Bai group combines theory and experiment in solid mechanics, materials science, and other multiphysical processes in areas including but not limited to multifunctional materials, fracture, adhesion, strengthening and toughening, sustainable materials, soft robotics, human-machine interfaces, and energy storage systems.

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