Mechanically Adaptive Materials and Structures by Coupled Mechanical Systems
Sung Hoon Kang
Department of Mechanical Engineering
Hopkins Extreme Materials Institute, Institute for NanoBioTechnology
Johns Hopkins University, Baltimore, MD
Friday, February 10, 2023, from 3:00–4:15 pm
Innovation Hall 207, Fairfax Campus, George Mason University
Live streaming at SciTech Campus- CEC Research Labs, Innovation Dr., Conference Room #106
Host: Pilgyu Kang
Adaptability is one of the hallmarks of living systems that provide resilience to survive and flourish in a dynamically changing environment. I will present our efforts to study coupled mechanical systems toward mechanically adaptive materials and structures. I will start with the overview of my research, then focus on two recent efforts. First, I will present self-adaptive materials that can change their mechanical properties depending on loading conditions by the coupling between loading and material synthesis. Nature produces outstanding materials for structural applications, such as bone and wood, that can adapt to their surrounding environment. For instance, bone regulates mineral quantity proportional to the amount of stress. It becomes stronger in locations subjected to higher mechanical loads. This capability leads to the formation of mechanically efficient structures for optimal biomechanical and energy-efficient performance. However, it has been challenging for synthetic materials to change and adapt their structures and properties to address the changing loading condition. To address the challenge, we are inspired by the findings that bones are formed by mineralizing ions from blood onto scaffolds. I will present a material system that triggers mineral deposition from ionic solutions on scaffolds upon mechanical loadings so that it can self-adapt to mechanical loadings. For example, the mineralization rate could be modulated by controlling the loading condition, and a 30-180% increase in the modulus of the material was observed upon cyclic loadings whose range and rate of the property change could be modulated by varying the loading condition. Moreover, the material system showed improved fatigue resistance from its damage mitigation mechanism . We envision that our findings open new strategies for making synthetic materials with self-adaptable mechanical properties. Second, I will present adaptive energy-absorbing “materials” with extreme energy dissipation and improving energy absorption with increasing strain rate by the coupling between viscoelasticity of materials and nonlinear geometrical effects. An architected material (or metamaterial) is a class of materials that provide new properties not observed in natural materials or from a bulk material that the “material” is made of. We utilize energy dissipation mechanisms across different length scales by using architected liquid crystalline elastomers. As a result, our energy-absorbing materials show about an order of magnitude higher energy absorption density at a quasi-static condition compared with the previous studies and even higher energy dissipation at faster strain rates with power-law relation, whose exponent can be tuned by controlling the mesoscale alignment of molecules using a simple strain control-based approach. We also found that we can further enhance the energy absorption density by vertical stacking due to viscoelasticity . The findings from our study can contribute to realizing extremely lightweight and high-energy-dissipating materials, which will be beneficial for various applications, including aerospace, automotive, and personal protection. We envision that our research can contribute to mechanical systems with embodied “intelligence”, leading to more resilient and sustainable systems with applications including aerospace, automotive, and healthcare.
Sung Hoon Kang is an Assistant Professor in the Department of Mechanical Engineering at Johns Hopkins University. He earned a Ph.D. degree in Applied Physics at Harvard University and M.S. and B.S. degrees in Materials Science and Engineering from MIT and Seoul National University, respectively. Sung Hoon has been investigating solutions to address current challenges in engineering materials, structures and devices with applications including resiliency, sensing, energy, and healthcare. In particular, he investigates behaviors of coupled mechanical systems by numerical modeling, nano/micro/macro fabrication, 3D printing, 3D structural/material/mechanical characterizations, and in vitro/in vivo testing. His research has been supported by AFOSR, NSF, NIH, ARO, ONR, State of Maryland, and private foundations. Throughout his career, Sung Hoon has co-authored 59 papers, has given over 180 presentations (including over 110 invited talks), and has six patents and five pending patents. His honors include 2023 Young Innovator Award by Nano Research, Invitee for First US-Africa Frontiers of Science, Engineering, and Medicine Symposium, 2022 Hanwha Non-Tenured Faculty Award, 2021, 2020 Air Force Summer Faculty Fellowship, 2020 Johns Hopkins University Catalyst Award, 2019 Johns Hopkins University Whiting School of Engineering Research Lab Excellence Award, Invitee for 2019 China-America Frontiers of Engineering Symposium, FY 2018 Air Force Office of Scientific Research Young Investigator Program Award, Invitee for 2016 National Academy of Engineering US Frontiers of Engineering Symposium, and 2011 Materials Research Society Graduate Students Gold Award. He served as an editorial board member of Scientific Reports and a guest editor of Materials Research Society Bulletin. Currently, he serves as an editorial board member of Multifunctional Materials and Sensors, respectively. He has been co-organizing ~35 symposia on bioinspired materials, 3D printing, and mechanical metamaterials at international conferences. He is a member of American Society of Mechanical Engineers (ASME), Materials Research Society (MRS), American Physical Society (APS), and Society of Engineering Science (SES). He served as the Chair, Vice Chair, Secretary, and Editor of ASME Technical Committee on Mechanics of Soft Materials.