Jinkyu Yang, Ph.D. - US grants

The research objective of this award is to simulate and measure the formation of acoustic solitons in two-dimensional granular waveguides. The PIs will design and fabricate hexagonally packed granular lattices "defined as granular phononic crystals" contained in a narrow channel. The PIs will unveil unique soliton formation and transmission mechanisms in the assembled granular architectures. The fundamental understanding of soliton propagation will enable a new class of waveguides that can filter, delay, and redirect acoustic solitons in a controllable and efficient manner. The PIs will achieve this research goal by developing an advanced discrete element model (DEM) and a novel digital image correlation (DIC) technique. Based on molecular dynamics techniques, the DEM will simulate the propagation of solitons under the full consideration of axial and rotational dynamics of tightly packed, frictional particles. The PIs will verify the numerical simulation results by the DIC techniques that measure extremely small particle displacements at high sampling rates.

From the viewpoint of physics, the findings in this study will contribute to the advancement of nonlinear mechanics of granular media based on the Lagrangian description of particle dynamics. With a view towards potential engineering applications, the fabricated solitonic waveguide can open a new paradigm in mechanical wave filtering, acoustic imaging, and nondestructive evaluation by leveraging an added degree of freedom in controlling mechanical waves. Besides contributing to science and engineering, the research activities will also have a broader impact on educating students. The PIs will recruit and train underrepresented students via student services and programs at the University of South Carolina (USC). The knowledge and product obtained from this work will be integrated into the new graduate program in aerospace engineering at USC.

X-ray computed tomography (CT) allows researchers to see inside structural, mechanical, electronic or biological parts and produce high-resolution 3D images of the parts, inside and out. This technology has evolved to enable X-ray CT scanning of larger parts made from denser materials while achieving high resolution at fast scan times. These advances have made x-ray CT a unique tool for researchers in disciplines from civil engineering to biology. This Major Research Instrumentation (MRI) award supports the acquisition of an advanced X-ray CT scanner capable of scanning parts as large as 1.2 meters tall and 0.84 meters wide at very high resolutions. A multidisciplinary team of University of Washington (UW) researchers has been assembled to acquire the instrument, including researchers from civil engineering, mechanical engineering, aeronautical engineering, anthropology, the Washington Nanofabrication Facility (WNF)/Electrical Engineering, biology, earth and space sciences, material science, and the Burke Museum which is a natural history and cultural museum on the campus of the University of Washington. The research enabled by this instrument is as broad and multidisciplinary as the research team and it will help to drive innovations in these diverse disciplines.

The imaging capability provided by the x-ray CT will allow structural engineering researchers to perform tests of large-scale structural subassemblages and then image the key components following the tests; enabling discovery of damage not visible from the surface. X-ray CT will be used to monitor damage progression in reinforced concrete bond zones, improving understanding and modeling of bond zone behavior. Researchers in composite structures used in aero, mechanical and civil applications will image composite components to investigate barely visible and subsurface defects, and failure initiation. These data will help develop and validate numerical models that rely on accurate characterization of voids and variations in fiber angles across laminate layers, advance composite micromechanics and failure theories for composites, and improve bond quality. Researchers in 3D printing will use the X-ray CT for nondestructive inspection of both internal and external geometry of 3D printed parts. They will also explore the effectiveness of X-ray CT evaluation of spatially controlled material composition of the 3D printed parts which is not otherwise feasible. Researchers in biological systems will image large portions of skeletal remains, fossils, and recently deceased animals to determine exact geometries; these data will enable the development of bio-mechanical models and investigation of the function of biological structures. Researchers in electrical engineering and nanofabrication will use the instrument in failure analysis of electronics fabricated with advanced techniques. The instrument will become a key piece of research infrastructure for the University of Washington and the Pacific Northwest.

This Faculty Early Career Development (CAREER) project aims at developing a new class of structural materials, also known as "phononic", whereby engineered nonlinear interactions suppress structure-borne noise and vibrations directly by manipulating the propagation of stress waves. This will be enabled by wave mixing effects inherent to the engineered nonlinear interactions that mimic phenomena observed at the atomic level. In transportation systems, structural components are susceptible to harsh mechanical environments, including vibrations, engine noise and aerodynamic/acoustic loads. The suppression of noise and vibration is highly critical, since it is associated directly with the long-term durability of mechanical/electrical components and the comfort level of passengers. Current techniques for noise reduction rely heavily on classical methods based on damping absorbers, such as soft foam, rubber wedges, and insulating blankets. While these methods are efficient in suppressing high frequency noise and vibrations, attenuation of low frequency components through a structure-borne path remains a formidable challenge. This research will contribute to the development of next-generation structural materials that are inherently capable of reducing structure-borne acoustic noise and rejecting unwanted vibrations in an efficient and controllable manner. From an educational standpoint, this project will attract young minds to science and engineering by enhancing their understanding of mechanical wave propagation through the "Catch a Wave" campaign.

This project involves designing, fabricating, and testing of a new type of engineered periodic lattices called "nonlinear phononic structures." These phononic structures will feature novel mechanisms that couple the propagation of different stress wave modes coherently. One example is a variable stiffness mechanism that leverages geometrical nonlinearities of thin-walled structures. These nonlinear phononic structures will naturally allow us to dynamically manipulate one stress wave mode via another, which is analogous to the working principles of electrical and optical energy flow devices (e.g., transistors). From a fundamental viewpoint, this project will shed light on the nonlinear wave dynamics of engineered lattice structures, leading to the discovery of new physical phenomena in terms of wave dispersion, disintegration, and scattering, unprecedented in conventional material systems and structures. From an engineering standpoint, the findings will open a new paradigm in filtering and mitigating structure-borne noise and vibration by dynamically controlling waves' speed, waveforms, and transmission gains.

One of the grand challenges in engineering, physics, and materials science is the ability to design materials with properties that do not occur in natural systems. Mechanical metamaterials attempt to achieve this by building an aggregate system out of linear or nonlinear components, that collectively exhibit material properties and functionalities that differ from, and surpass those of, their constituent materials. However, their functionality is typically compromised by defects and imperfections, which are unavoidable in real world applications. This begs the question of whether a new paradigm exists, whereby a new class of building blocks and interactions enables the design of materials that are robust to imperfections and that are characterized by new functionalities. These studies will demonstrate that concepts from topology provide an organizing principle that gives rise to a wide range of impurity-immune phenomena in areas such as wave guiding, structural stability, and fracture. The project findings will have implications for the design and fabrication of mechanical energy control systems and devices whose operation relies on wave focusing, amplification, localization and attenuation. These include ultrasonic acoustic transducers, sonars, noise absorbing or enhancing devices, and material systems for vibration filtering and impact/blast protection. The objectives of the project will be achieved through the collaboration of a team that combines experts in topological mechanical metamaterials, experimental wave dynamics, linear and nonlinear wave propagation, condensed matter physics and mathematics. This multi-disciplinary approach to research is rich in opportunities for outreach and for broadening participation of underrepresented groups in engineering and science. For example, outreach programs to underrepresented groups will be organized in collaboration with the Museum of Science and Industry in Chicago.

This project investigates topological mechanical metamaterials that challenge classical notions in mechanics such as reciprocity, time reversal symmetry and sensitivity to defects. The objective is to investigate their fundamental properties, such as the existence of topological modes in ordered, disordered and amorphous systems, the effects of nonlinearities, as well as energy transport in the bulk. Guided by these studies, the research team will then explore the engineering implications of topological mechanical metamaterials, focusing on wave guiding, structural stability and fracture. These investigations will be conducted on novel experimental platforms ranging from gyroscopic systems as proof-of-concepts, to newly designed continuous systems that have potential for material/structural system development. The research is expected to enable functionalities that shift the paradigm in which dynamic control devices and materials are designed. The team's unique strengths in theory, simulation and experiments provide the combination of skills that are essential for the successful execution of this ambitious research program.

Corals are important natural resources that are key to the ocean's vast biodiversity and provide economic, cultural, and scientific benefits. As a result of human activities, locally and globally, coral reefs are declining rapidly. The complexity of corals makes conserving and restoring reefs very challenging. Corals are made up of thousands of different organisms, including the animal host and the algae, bacteria, viruses, and fungi that coexist as a so-called holobiont. Thus, corals are more like cities than individual animals, as they provide factories, housing, restaurants, nurseries, and more for an entire ecosystem. This project brings together experts in computer science, materials science, and biology to harness the data revolution in biology with machine learning to study how corals grow and function, when viewed as if they were manufacturing sites in the ocean. The study will focus on three key coral capabilities: (1) they create calcium carbonate skeletons that provide 3D structures for diverse sea life to live in, (2) they can heal damage to their tissues, and, (3) they live with the other organisms in a process referred to as symbiosis. Through these remarkable abilities, corals can 'print' resources for themselves and hundreds of thousands of other species, just like a 3D printer. The goal of this project is to understand these processes well enough to control them in the lab. This project may allow finding new ways to help coral survival, by deciphering the reasons why certain conditions damage them and find ways of repairing them. Furthermore, by synthetically growing corals, new types of materials may be identified for manufacturing. This project offers an opportunity to educate a diverse scientific workforce and the public by creating and disseminating the outcomes of a convergent research environment and will train postdoctoral researchers, graduate, and undergraduate students. Results of this research will be made available to the broader scientific community through web interfaces, peer-reviewed publications and workshops/conferences and shared with the public through outreach activities online, at schools, and public aquariums.

Through convergence of three disciplines, computer science, material science and biology, this project will provide a data-driven framework and toolset to learn from, control, engineer, and manufacture a combined form of living material, the 'synthetic coral', thereby opening new avenues for material synthesis and manufacturing. The research methodology will offer new analytical approaches to identify and quantify the parameters that govern coral growth and foster innovative new tools for controlling their growth. To understand the key functions of coral biology of biomineralization, wound healing, and symbiosis, this research will : (1) harness and analyze large amounts of coral '-omics' data to decipher critical molecules and their interactions for the aforementioned key functions, (2) experimentally validate the resulting predictions in coral individuals and cell lines, (3) manipulate the material properties of the calcium carbonate structures of the coral individuals and cell lines, and (4) test the biological and physical interactions in a network model of the 'synthetic coral'. This project develops and integrates fundamental building blocks that are essential for an integrated computational and experimental validation system. Specifically, using machine learning, diverse data will be harnessed to identify physical conditions (e.g., surface characteristics), environmental conditions (e.g., temperature, pH), and key biological constituents (e.g., small molecule ligands and proteins encoded in the DNA) that are correlated to key structural and functional properties of the coral holobiont. These predicted conditions and molecules will be verified experimentally by perturbing individual coral nodes in a network of a 3D printed array of intact corals or their constituent cells and measuring their effects on the network of interactions and resulting structures. The results from this prediction-validation cycle will then be transferred back as input to manufacture novel adaptive materials fully embracing the organic/inorganic interface.

This project is part of the National Science Foundation's Harnessing the Data Revolution (HDR) Big Idea activity.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

The research objective of this award is to provide the needed knowledge for the formation of rogue waves in mechanical structures. Rogue waves are abnormally large-amplitude waves that appear abruptly and disappear without the trace. Rogue waves in the ocean, often referred to as the ?wall of the water,? have been witnessed by seafarers. However, the existence of such waves that swallow big ships in the ocean has been mythical for a long time. It is only a couple of decades ago that their existence has been verified scientifically. Since then, rogue waves have been a subject of intense research in different media. Nonetheless, the realization of mechanical rogue waves in solids and structures remains elusive to date. The quest for such mechanical rogue waves in engineered lattices constitutes the core of this project. The successful formation of mechanical rogue waves will enable scientists and engineers to focus mechanical energy in an efficient and controllable manner. Thus, the findings from this project can open a new avenue to guiding high-amplitude mechanical wave packets, harvesting ambient mechanical energy, and developing novel sensing/actuation systems. From an engineering standpoint, this new mechanism of mechanical energy control can be applied to aerospace, mechanical, and civil industries, thereby benefiting society. From an educational standpoint, this project will help train young minds, including several underrepresented students, in the field of science and engineering.

The manipulation of mechanical energy flow (i.e., mechanical waves) is challenging. Particularly, the controllable localization of mechanical energy demands new technical approaches beyond the utilization of conventional linear elastic wave principles. This project will introduce the concept of rogue wave generation, the focusing mechanism of waves mostly observed in fluidic or optical media, to the mechanical realm. As an analytical guideline, the celebrated nonlinear Schr?dinger equation will be applied to one-dimensional mechanical lattices (i.e., nonlinear spring mass systems like Fermi-Pasta-Ulam-Tsingou lattices). Based on this analysis, computational models of dynamic lattices will be established in a form that facilitate the formation of mechanical rogue waves. Lastly, a prototypical system will be fabricated using 1D discrete lattices. The formation of mechanical rogue waves will be verified by conducting full-field measurements of the prototype?s wave dynamics using action camera-based stereo vision techniques. All components of these analytical, computational, and experimental studies will be integrated into the education and training of participating undergraduate and graduate students.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Origami-inspired structures that fold flat sheets along creases with designed patterns to create transformable structures have been widely applied in science and engineering, especially in space operations, e.g., for deployment of folded solar panels equipped on launched satellites. Although the deformation process plays an essential role in transitions between the origami states, few studies focus on the control and actuation of the origami folding mechanism toward high autonomy of the deformation process. This project aims to develop an autonomous origami-inspired transformable system to enable high-performance deformation maneuvering in space operations requiring frequent and/or time-responsive shape changes. The integrative research incorporating theory, analysis, algorithm development, and experimental verification will contribute to a theoretical and experimental platform to advance the autonomy of origami system operations in challenging environments. The research products will have significant impacts on the proliferated satellite marketplace where low mass, small volume, and adaptable structures/subsystems of space vehicles are in demand. Going beyond the applications in space missions, origami-inspired transformable systems have much broader applications in science and engineering. Moreover, the collaboration of experts in both cyber and physical areas promotes the creation of interdisciplinary products that bridge different disciplines.<br/><br/>To achieve the research goal of advancing autonomy of origami-inspired transformable systems, four research thrusts are identified, namely (1) developing a network-based approach for modeling and design of multi-shape origami structures, (2) designing an integrated sensing and control strategy with guaranteed controllability, reachability, and energy efficiency, (3) developing programmable untethered actuation via thermal loading to realize designed control maneuvers, and (4) evaluating the performance of autonomous systems using multiple origami structures in space operation missions. These identified research thrusts will together contribute to an analytical and computational framework for achieving autonomy of the origami deformation process, which will result in real-world applications in future space missions. Theoretically, the fundamental analysis based on networked control and graph modeling can lead to rigorous support of control performance in terms of controllability, reachability, and energy efficiency for the origami deformation process. Practically, the development of programmable untethered actuation enables the generation of designed control commands under operational constraints.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.