Soft actuators
Unlike rigid robotic actuators, soft robotic actuators are made of lightweight and often soft material which can provide large strokes with high degrees of freedom, without the need for hinges or sliding mechanisms. In addition, with stiffness values comparable to biological systems, they can more readily interact with humans without damage. The artificial muscles change dimensions in response to various stimuli such as heat, electricity and chemical reactions, and the change in dimensions can be presented as the relative change in length (linear stroke) along a specific direction or relative change in volume. However, a recent body of work has been devoted to amplifying the actuation stroke of artificial muscles in a particular direction by benefiting from the dimensional changes in the directions that are orthogonal to the actuation stroke. In this line of research, we aim at developing novel materials and material architectures that enables agile soft actuation with high work capacity.
This research is sponsored by Army Research Labs.
Mechanics of nanostructured ceramics
The re-emergence of hypersonic transport applications in the past few years has once again demonstrated the need for developing materials which can carry load at ultra-high temperatures even in excess of 2000ºC. While ceramics and ceramic-based composites withstand high temperatures, their low fracture toughness make them susceptible to damages. Our research goal is to establish a systematic understanding of toughening mechanisms in relation to processing in heterogeneous pyrolyzed-sintered ceramics with a focus on the toughening mechanisms due to heterogeneities along interfaces of different phases and inclusions. Our material system will consist of three distinct phases which provide ample opportunities to enhance the toughness: (I) sintered ceramic particles, (II) polymer-derived ceramic (PDC) which acts as the “glue” in between the particles of phase I and also matrix for (III) the 1D/2D nanofillers (mostly passive). The toughening mechanisms targeted include energy dissipation events such as nanomaterial pull out (nanoscale) and crack path deflection (micro and nanoscale), as well crack tip entrapment at low elastic energy areas by means of heterogeneity at larger length scales. To achieve the goal, we will develop a general processing method, assisted with multiscale modeling and big data, for embedding various nano-reinforcement into ceramic matrices (e.g., carbides and borides), and we will study the effect of heterogeneities on load bearing performance metrics, toughness and strength at a wide range of temperatures.
This research is funded by office of Naval Research.
Processing-performance in vitrimer-based composites
This study focuses on vitrimer-based fiber composites. The vast majority of polymers used as matrix in polymer composites fall into one of the two categories: The commonly used thermosets with non-reversible crosslinks and thermoplastics. Recently, vitrimer polymers (Science, 2011) were introduced that have desirable properties of both common thermosets and thermoplastics. While vitrimers are technically thermosets, i.e., they form covalent networks upon curing which is desired for load bearing, their network can reconfigure to enable intrinsic self-repair, reshaping of parts, and even recycling. The bond exchange occurs in response to thermal and mechanical stimuli without sacrificing part integrity, which is a clear advantage over other reformable mechanisms, e.g., depolymerization–repolymerization. Despite the advantages of using vitrimers for composites, our understanding of the dependencies of the mechanics of their composites on molecular traits of vitrimers as well as best practices for minimizing manufacturing defects by relying on exchangeable bonds are largely unknown. To address this gap, we aim at evaluating the mechanics of vitrimer composites at a wide range of temperatures in relation to molecular traits of vitrimers such as the flexibility of the chains and their ability to form long-range order.
This research is sponsored by Air Force Office of Scientific Research.
Additive manufacturing of high performance polymers
We are exploring novel additive manufacturing methods for high performance polymers by means of medium-enabled printing. The content of this research is proprietary.
This research is sponsored by Army Research Labs.
Mechanics of Mixed-dimensional nanomaterials
Materials that exhibit superior energy dissipation in response to tearing and impact are highly desired for armors and protective clothing. A class of promising candidates for such applications is hybrid 1D-2D nanomaterials where 1D materials (i.e., rebars such as nanowires) are used as reinforcements of 2D materials, e.g., graphene. Here, the 1D nanomaterials are used to reinforce the 2D material against defects. However, it is not clear yet how the energy dissipation in such hybrid nanomaterial depends on the 1D-2D material interfaces and rebar arrangement. For instance, the interface bonding will likely affect the size of the interfacial transition zone (ITZ) during crack propagation with significant yet unknown effects on toughness and strength. The ITZ is the region of 2D material in the vicinity of the rebar with a unique deformation mode such as microbuckling and excessive shear deformation. This uncertainty hampers meaningful progress in the field.
Striving to address this knowledge gap, the goal of this project is to unravel the dependence of emerging crack patterns, impact energy dissipation, and size of the damaged zone on 1D-2D interfacial mechanical behavior and arrangement of 1D rebars in a carbon nanofiber (CNF)-graphene hybrid structure under quasi-static and dynamic loading.
This research is funded by Army Research Office.
Electrification of Aircraft
The aviation sector accounts for 9.3% of total US transportation sector CO2-equivalent emissions. More than 28% of United States and 14% of global greenhouse gas (GHG) emissions originated from the transportation sector in 2018. Rapid growth in revenue passenger kilometres (RPK) estimated at 4.45% globally and 3.10% in North America will more than triple RPK by 2050 leading to significant growth in aviation sector emissions. Despite projected improvements in aircraft fuel efficiency and reductions in aircraft emissions over upcoming decades, total
aviation sector emissions are projected to grow more than 50% by 2050, accounting for nearly 5% of total US emissions, which displays net CO2 emissions on absolute (million metric tons (MMT)) and percentile bases using data from the US Energy Information Administration’s Annual Energy Outlook in 2022. This growth in sector emissions further motivates the necessity of transitioning to reduced-emissions technology for the aviation sector. This work aims to identify innovative ways by which electrification of airplanes may take place in the next 2-3 decades.