Abstract: Materials with superior specific energy absorption, -strength, and -stiffness are critical for lightweight protective helmet liners, sports gears, and vibration dampers. The vertically aligned carbon nanotube (VACNT) foams provide us with an opportunity to tailor the structure of individual CNTs and their organization across multiple length scales from micro to macroscales to achieve desired bulk properties. By exploiting size-confined synthesis of architected VACNT foams and interactive morphology from the mesoscale architected elements, we show that the specific modulus, -strength, and -energy absorption of VACNT foams can synergistically be improved. We further exploit the different structural buckling modes in design to tailor the density-dependent scaling laws to create ultra-low-density materials with superior specific energy absorption. The dissipation, on the other hand, is considered undesirable when designing actuators or metamaterials for high-quality wave guiding. In contrast, we demonstrate an unusual reconfigurable enhancement in actuation force using engineered damping in a novel non-Hermitian metamaterial. The actuation force is enhanced up to twofold of its expected value 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.

BIO: 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 2024 Vilas Faculty Early Career Investigator Award from UW-Madison, 2022 Early Career Faculty Award from NASA, 2022 Innovation Award from the Wisconsin Alumni Research Foundation, and 2021 Ferdinand P. Beer and E. Russel Johnston, Jr. Outstanding New Mechanics Educator Award from the American Society for Engineering Education