Recently Funded Projects by Junior Faculty

Characterization of Hydrodynamics and Behavior of Viscoelasticity at the Nanoscale

  • PI: Assistant Professor Ryan Tung
  • $332,204, National Science Foundation

The objective of this project is to understand the effect that complex sample viscoelasticity and hydrodynamic forces at the nanoscale have on the resonant behavior of measurement systems by developing mathematical and numerical models that capture and quantify these phenomena. The completed project will enable, for the first time, accurate contact resonance based quantitative nanomechanical characterization of biological materials in liquid environments using atomic force microscopy.

Project abstract

The ability to measure physical properties of materials at very small scales is key to advancing scientific research and technological progress. Measurements that occur at the nanoscale, where the physical dimensions involved are on the order of one billionth of a meter, are of particular importance. The atomic force microscope (AFM) is one of the primary tools for making quantitative measurements of material properties at the nanoscale. However, there exist many physical phenomena at the nanoscale that prevent accurate quantitative measurements from being made - especially in liquid environments. This project aims to understand and fully characterize two such phenomena: fluid forces that arise at the nanoscale when the AFM is operated in liquid environments (hydrodynamics) and the underlying principles that govern the behavior of the material being interrogated (viscoelasticity). This project will enable quantitative measurements of material properties at the nanoscale in liquid environments on a variety of inorganic and biological materials. This will enable new and cutting-edge research in areas such as medicine, biology, and materials engineering. In addition, the project's educational plan will develop a hands-on, interactive, and portable learning platform that will expose K-12, undergraduate, and graduate students to AFM and the scientific principles used in its operation. The educational plan will engender further interest and retention in the STEM fields.

The objective of this project is to understand the effect that complex sample viscoelasticity and hydrodynamic forces at the nanoscale have on the resonant behavior of measurement systems by developing mathematical and numerical models that capture and quantify these phenomena. These effects can be addressed through the lens of contact resonance (CR) spectroscopy AFM. The CR spectroscopy system is an ideal measurement platform to understand these phenomena because it is well understood in the absence of these effects and has the ability to interrogate both the hydrodynamic and viscoelastic parameter spaces of interest. The objective of the project will be accomplished by pursuing the following specific tasks: 1) accurately predicting the three-dimensional fluid-structure interactions present in CR spectroscopy systems, 2) establishing material models for CR spectroscopy to account for biological and non-classical viscoelastic materials, and 3) experimentally validating the fluid-structure interaction and viscoelastic models. The completed project will enable, for the first time, accurate contact resonance based quantitative nanomechanical characterization of biological materials in liquid environments using atomic force microscopy. This, in turn, will enable research in several key areas. These areas include accurate characterization of mechanical properties of stimuli-responsive polymer nanocomposites with applications to the medical community, the study of nanomechanical structural changes in osteoarthritic bone to help determine the underlying phenomena of osteoarthritis, the study of dentin and tooth enamel, and the study of biomaterials and bio-polymers.

Collaboration Research: Exploiting tunable stiffness for dynamic adhesion control at the macro and micro scale

  • PI: Assistant Professor Wanliang Shan
  • $355,610, National Science Foundation

This collaborative award totaling $625k for UNR (lead institution, $356k) and Penn ($269k) is based on the idea of using smart materials to realize soft composite structures exhibiting dynamically tunable dry adhesion, a new concept that revolutionizes the field of tunable dry adhesion.

Project abstract

Surfaces with dynamically switchable adhesion have a wide range of applications in fields such as robotics and manufacturing. For example, surfaces with switchable adhesion enable new types of gripping surfaces for use in climbing and perching robots. This award supports research to realize a new concept in switchable adhesive surfaces based on the use of composite materials where the stiffness of one component of the material can be changed via the application of an electrical signal. By modulating the stiffness of one component of the composite, the manner in which force is distributed to the interface is altered, and as a result, the effective adhesion strength of the interface is changed. The underlying adhesion mechanics of these materials will be established through modeling and experiments, thus enabling the optimized design of composite structures with dynamically switchable adhesion. This project is a collaboration between researchers at the University of Nevada, Reno and the University of Pennsylvania and will result in the training of students in advanced materials, mechanics, manufacturing, and soft robotics, thus contributing to the development of the engineering workforce in the U.S.

The research will realize new composite materials with dynamically tunable adhesion through a research plan that includes the design, fabrication, and characterization of two classes of elastomer-based composite materials with high dry adhesion strength. Finite element-based multiphysics models will be used to investigate the how the structure of the composite and the stiffness heterogeneity contribute to the effective adhesion strength. Scalable routes to realize flat and fibrillar surfaces made of these composite materials will be developed by leveraging microfabrication techniques and recent manufacturing advances from the field of soft robotics and electronics. Characterization efforts will focus on establishing the mechanical and adhesion properties of the constituent materials in order to inform the modeling and simulation effort and the adhesion properties and performance of the novel composite material systems that are fabricated. This research will lead to an improved fundamental understanding of the mechanics and manufacturing of composite material systems with tunable adhesion.

Development and Experimental Benchmark of Simulations to Predict Used Nuclear Fuel Cladding Temperatures during Drying and Transfer Operations

  • Research Scientist Mustafa Hadj Nacer Co-PI (w/M. Greiner)
  • $399,754 total, ($149,754, Dr. Hadj Nacer's portion) Department of Energy

Radial hydride formation in high-burnup used nuclear fuel cladding has the potential to radically reduce its ductility and suitability for long-term storage and eventual transport. To avoid this formation, the maximum post-reactor temperature must remain below certain values to limit the cladding hoop stress, and assure that hydrogen from the existing circumferential hydrides will not dissolve, making it available to re-precipitate as radial hydrides under the slow cooling conditions that exist during long-term dry-cask storage. The claddings may reach their highest temperature during drying processes of nuclear canister. The objective of the proposed research is to develop tools that will aid to design efficient drying processes that effectively and rapidly remove moister while maintain cladding temperatures below safe limits.

Project abstract

Used light water reactor fuel rods consist primarily of zircaloy cladding tubes that contain highly radioactive fuel pellets and high pressure gases. After being discharged from reactors, nuclear fuel assemblies are stored underwater while their radioactivity and heat generation rate decrease. After sufficient time, a canister with an internal basket is placed in a transfer cask and lowered into the pool. The canister is then loaded with fuel assemblies, covered, lifted out of the pool, and drained while helium or another inert gas flows in. Small amounts of water may remain at the bottom of the canister and in crevices of the fuel and basket. Most of all remaining water must be removed to reduce the probability of corrosion or formation of combustible gases. The canister is then filled with helium and sealed, for onsite dry cask storage or offsite transport.

The claddings may experience their highest temperature during drying process because this is the first time they are removed from a water-cooled environment, and their heat generation rate is still relatively high. This increases the hydrogen solubility limit and causes the existing hydrides to dissolve. Moreover, the gas pressure in the canister is significantly lower than the pressure within the cladding tubes, which leads to large cladding hoop stresses. Later, during long-term storage, as the fuel heat generation rate decreases, the fuel temperature slowly declines, causing the hoop stress and hydrogen solubility within the cladding to simultaneously decrease. If the initial hoop stress is sufficiently high, the precipitating hydrogen will form radial hydrides. Hydrides in this orientation embrittle the cladding and increase the likelihood of failure under drop accidents during handling and transportation.

The objective of the proposed research is to develop and experimentally-benchmark computational fluid dynamics simulations (CFD) of heat transfer and vapor transport in cask drying operations, when high-burnup fuel claddings are likely to experience their highest temperature. The benchmarked tools will aid the design of efficient drying processes that effectively and rapidly remove moister while maintain cladding temperatures below safe limits.

Modeling and Design of Enhanced Strength and Ductility though Grain Boundary Engineering-A study of Boron Carbide Based Superhard Materials

  • Assistant Professor Lei Cao Co-PI (PI: Q. An)
  • $476,410 ($238,205, Dr. Cao's portion), National Science Foundation

The low ductility of boron carbide, a so-called superhard ceramic, greatly limits its use in a vast array of engineering applications, such as cutting tools, body armor for soldiers, and manufacturing processes. This project will use multiscale simulations that couple atomistic modeling and the mesoscale phase-field method to first investigate the impact of grain boundaries on mechanical properties, deformation, and failure mechanisms and second establish design principles to enhance the strength and ductility of boron carbide through grain boundaries microalloying. The design strategies that will be developed in this research will be extendable to a variety of other superhard materials, such as borides, carbides, and diamond.

Project abstract

Strength refers to a material's ability to withstand failure or yield, while ductility is its ability to permanently deform without fracture. Many important engineering applications require high strength and yet ductile materials, such as in cutting tools, body armor for soldiers, and manufacturing process. One promising candidate is boron carbide, a so-called superhard ceramic names so because of its strength; however, it has low ductility. In poly-crystalline materials, the strength and ductility are commonly associated with microstructural features at the lower length scales (micrometers and below). There is a significant knowledge gap regarding the impact of microstructure on the strength and ductility of superhard ceramics. This project is directed towards the study of the physical mechanisms that underlie the relationships between microstructure, and strength and ductility of boron carbide based materials using computational modeling and simulations. The project will also establish design principles based on the knowledge gained for the development of new boron carbide based materials with enhanced strength and ductility. The design strategies will be extendable to a variety of other superhard materials, such as borides, carbides, and diamond. The research will be integrated into both undergraduate and graduate education, as well as outreach activities for local high school students. The research project will also target the participation of women and under-represented minority students in science, technology, engineering, and math disciplines. The research objective of this project is to illustrate how microstructure determines the deformation and mechanical processes in boron carbide based materials. The research team will apply a multiscale approach coupling atomistic modeling and the mesoscale phase field method to  investigate the impact of grain boundaries on mechanical properties, deformation, and failure mechanisms of boron carbide and establish the design principles to enhance the strength and ductility of boron carbide through engineering of grain boundary properties with microalloying. The research will make original contributions in elucidating the origins of the strength and ductility of polycrystalline superhard ceramics under realistic conditions. The materials design principles will be applied to inspire experimental synthesis of stronger and tougher boron carbide based materials for commercial applications.