Title: An Ally in Dissipation: From Effective Impact Mitigation to Enhanced Actuation through Engineered Dissipation

Biography: Prof. Ramathasan Thevamaran received his B.Sc.Eng.(Hons.) (2008) in Civil Engineering from the University of Peradeniya, Sri Lanka, and his M.S. (2010) and Ph.D. (2015) in Mechanical Engineering from the California Institute of Technology, CA. Prior to joining the University of Wisconsin-Madison in 2017, he was a Postdoctoral Research Associate at the Department of Materials Science and Nanoengineering of Rice University, TX. His research focuses on (i) developing a fundamental understanding of the process-structure-property-function relations in structured materials, and (ii) creating innovative structured materials with superior specific properties and novel functionalities for extreme engineering applications. He is the recipient of the 2022 Early Career Faculty Award from NASA, and the 2021 Ferdinand P. Beer and E. Russel Johnston, Jr. Outstanding New Mechanics Educator Award from the American Society for Engineering Education.

Abstract:

Superior specific energy absorption, strength, and stiffness are critical for protective materials that are used in lightweight armor and spacecraft. Nanofibrous materials offer an opportunity to synergistically exploit intrinsic nanofiber properties and inter-fiber interactions for dynamic performance enhancement. We show synergistic performance improvement with failure retardation in carbon nanotube (CNT) mats by augmenting the weak van der Waal interactions with stronger and reconfigurable interfacial hydrogen bonds formed by introducing aramid nanofiber (ANF) links between CNTs. Under supersonic microprojectile impacts, strengthened dynamic interactions in ANF-CNT mats enhance their specific energy absorption up to 3.6 MJ/kg--outperforming other nanomaterials and widely used bulk Kevlar fiber-based protective materials.

The dissipation, on the other hand, is undesirable when designing actuators or metamaterials for high-quality wave transmission. In contrast, we demonstrate a reconfigurable enhancement in actuation force using engineered dissipative elements in a non-Hermitian metamaterial. The actuation force is enhanced up to twofold at a constant quality factor when we bring the system to operate at the proximity to an exceptional point--a singularity where the eigenvalues of a system and its corresponding eigenvectors coalesce. The ability to enhance forces by virtue of an engineered passive material can lead to lightweight autonomous actuation devices.