|Available Research Projects|
Piezoelectric materials can convert mechanical energy such as vibrations into electrical energy and are therefore being used for continuous energy harvesting from ambient vibrations. Such materials can be used to power infrastructure sensors and sensor networks without the need for replacement of batteries or wiring. In order to achieve optimal energy conversion efficiency, the resonance of the piezoelectric material device should be nearly equal to the input vibrational frequency. For infrastructure materials with relatively low ambient frequencies, the piezoelectric device should have a correspondingly low resonant frequency. This can be achieved by modifying the mechanical design of the piezoelectric device. The present project consists of two components related to both the input frequencies available and the optimal device design to use with these frequencies. The student will build and/or obtain a frequency monitoring device and use this device to measure the ambient vibrational frequencies of typical infrastructure materials, e.g. buildings or roadways. In parallel, the student will also examine several different mechanical design strategies for lowering the resonance frequencies of piezoelectric devices. This includes the evaluation of bender actuators of various size, shape, and mass, as well as other operational modes. At the conclusion of the project, the student will suggest the optimal piezoelectric device design for harvesting ambient vibrational energy from infrastructure materials.
The properties of infrastructure materials are largely dictated by their crystallographic structure. For example, the polymorphism of tricalcium silicate is strongly known to influence its mechanical strength. Advances in X-ray and neutron scattering techniques have created a wealth of new knowledge concerning the crystallographic structure of infrastructure materials, in particular the crystallographic structure during and after processing (e.g., hydration, dehydration). However, well-developed diffraction strain measurement techniques which have been used extensively to study the structural behavior of engineering materials, have not been widely applied to investigate the mechanical behavior of infrastructure materials. Such techniques can measure the crystallographic elastic and plastic deformation behavior during mechanical loading. The lack of application of such methods was recently highlighted in the work by Skibsted and Hall. This REU project will demonstrate the feasibility of these characterization techniques for in situ studies of elastic and plastic deformation behavior of infrastructure materials. The material to be investigated will be tricalcium silicate, a major constituent in Portland cement clinker. Powder materials will first be investigated by laboratory X-ray diffraction at the University of Florida. The student will be mentored by Jones and his research team in the use of crystallographic refinement (e.g., the Rietveld method) to confirm the crystal structure at room temperature. The student will then determine the crystallographic structure as a function of hydrostatic pressure using high-pressure neutron diffraction at the Oak Ridge National Laboratory. A postdoc on Jones’ team is partially supported by ORNL and is located at ORNL during a large portion of the year. This postdoc will mentor the student and will facilitate these measurements. These high-pressure measurements will enable the structure to be determined as a function of isostatic stress, a precursor to the measurement of this material under multiaxial stress states using instrumentation such as VULCAN at the Spallation Neutron Source (SNS).
Glass-ceramics in the Wollastonite family of compounds offer unique optical and mechanical properties that make them ideal for large scale production and for use as cladding in the building industry. An example of this is the commercial glass-ceramic Neoparies. As a building material it shows high wear and weather resistance with zero water absorption rate and it is harder and lighter than natural stone, and it is easy to shape. In this REU projects student will learn how prepare Wollastonite glass-ceramics compositions and will investigate the crystallization (nucleation and growth) of the ceramic phases within the glass matrix as a function of time and temperature. They will also correlate the resulting microstructure of the glass-ceramic with the electrical, mechanical and optical properties.
Structural health monitoring (SHM) entails much uncertainty due to the uncertain nature of the sensor data, modeling errors, and material and geometric properties. Therefore, a probabilistic framework is a key to efficient design and implementation of SHM. Furthermore, with continual flow of information about damage initiation and damage propagation extracted from raw sensor data measured on the structural components, a probabilistic framework should allow an SHM system to progressively improve the accuracy of both diagnosis and prognosis. The project involves a comparison study between two popular methods in identifying system parameters: least-squares and Bayesian inference. Using a same set of SHM data, the system parameters will be identified statistically, from which the remaining useful life (RUL) of the system will be predicted. The objective is to evaluate the performance of two methods in terms of reducing uncertainty in system parameters and RUL.
The goal of the project is to develop robust energy harvesters for monitoring road/bridge integrity that are embedded in the elastomer sealant located in the expansion joints in concrete pavements and on bridges (via rumble strips) which collect energy from asynchronous compression during wheel passage. There is a need for power sources for sensors and related electronics used for monitoring road/bridge integrity. Although solar energy is an option, it cannot be relied upon in situations where solar panels are not easily deployed or when solar exposure is limited. However, a constant in roadways is vehicular traffic. The proposed project employs mechanical energy harvesting using a novel asynchronous impulse based approach in a completely sealed structure. Mechanical energy harvesting has primarily focused on harvesting vibrational energy using resonant cantilever beams with a proof mass. However, the main drawback is the limited available energy in vibrations (typically on the order of milliwatts) and the sharp fall-off in harvested energy when the vibration frequency deviates from the resonant frequency of the cantilever beam. The proposed approach avoids the limitations of resonant energy harvesting by employing the force impulse from compression by tire passage for asynchronous deflection of symmetric beams embedded in an elastomer. The amount of available power is expected to be significantly higher since the tire passage load is much higher than the inertial load and is proportional to the load and the number of impulses per unit time. A prototype embedded asynchronous impulse-based energy harvester will be developed with interface electronics using conventional machining with bulk commercially available piezoelectric materials. The available energy will be quantified and sensor configurations will be evaluated.
This project will focus on developing techniques to fabricate novel composite particles on a single nanoparticle or nanofiber. These composites will have applications in building health and gas sensing applications. This project will investigate structure-property-processing correlations, where the student will synthesize materials and characterize them using a variety of tools including X-ray diffraction, electron microscopy, and magnetic measurements.
This research is aimed to investigate a solid-state joining method, pulsed magnetic welding (PMW), for welding the advanced core and cladding steels to be used in Gen IV reactor systems. The advanced core and fuel cladding steels developed for Gen IV reactor have a specially tailored microstructure, improved high temperature strength and exceptional radiation damage resistance. However, a potential issue that directly affects the field applications of advanced steels is the change in properties associated with the alteration of microstructures by conventional welding technologies. Since the superior properties depend on the uniform tempered martensitic microstructure for F/M steels and evenly distributed nano-sized oxide particles and precipitates for ODS and HT-UPS respectively, any changes induced by welding may be deleterious. Developing welding techniques that limit microstructural alteration is critical. The pulsed magnetic welding as a solid state welding technology with no melts and a minimal welding zone seems to be very promising. Currently, the work pieces of advanced steels have been fabricated and will be sent to PST at Germany for welding and optimization. It is planned to receive the weldments by April 2012. The proposed summer research activities will be focused on the post welding examinations including welding microstructure studies, leak test and mechanical test.
Dr. Sodano's group is pursuing the development of biologically inspired materials that can autonomously adapt to their current state or surroundings through adaptation, self-healing and stimulus responsive behavior. The past few years have seen a surge of research into autonomous materials; however, the resulting techniques are completely passive, cannot sense the presence of damage to allow a controlled response and cannot be performed during operation. To ensure that the structure’s health is maintained, it is imperative that viable methodologies be developed that evaluate the state of the structure while simultaneously providing a means to mitigate damage and recover the material’s properties. Here, polymers incorporating pendent cinnamate moieties that undergo efficient photoreversible cycloaddition reactions will be developed. A fiber optic network will be used to signal damage and apply controlled wavelengths of light at the damage site to allow local adaptation to toughen the material following by shape recovery and healing using photodimerization. Past healing modalities have not acted to stop the propagation of damage or signal its presence. This basic research effort will ultimately provide a paradigm shift in the synthesis and implementation of autonomously responsive materials and create structures that respond to damage as biological systems do.
The use of piezoceramic materials for structural actuation is a fairly well developed practice that has found use in a wide variety of applications. However, just as advanced composites offer numerous benefits over traditional engineering materials for structural design, actuators that utilize the active properties of piezoelectric fibers can improve upon many of the limitations encountered when using monolithic piezoceramic devices. The proposed research program will seek to create new synthesis, modeling and characterization approaches for the development of multifunctional materials that utilize a carbon fiber coated with a piezoelectric material. The research will specifically develop two novel processes for the conformal deposition of piezoceramic materials on carbon fiber while in a tow consisting of thousands of fibers. This novel fiber would make advances in the safety and performance of modern structures through the intelligent integration of sensing, actuation and energy harvesting into the material.
It has been shown by previous research that the failure mode of externally FRP reinforced concrete changes from cohesive (failure in the concrete layer) to adhesive (failure in the adhesive or in the interfacial failure between the adhesive and concrete) when such systems are exposed to moist conditions. The purpose of this project is to determine the moisture diffusion mechanisms that affect the bond strength and failure modes of externally applied FRP reinforcement. In order to determine the effects of moisture diffusion three types of specimens will be prepared and tested: (1) concrete specimen with a layer of Plexiglas adhered by epoxy to the bond area (to determine the water penetration through the concrete and its effects on the epoxy layer); (2) concrete specimen painted with a waterproof paint with a bond area exposed to a moist environment (in order to determine the water diffusion through the bond region); and (3) GFRP and CFRP fabric saturated by epoxy and subjected to the moist conditions (to determine the effect of fibers on epoxy moisture diffusion). The change in weight of exposed specimens will be monitored over the time in order to determine the water contents.
The purpose of this test is to determine the fracture energy in Mode II loading required to produce the adhesive failure of 2 in. mortar cubes and to correlate it to the fracture surface roughness. Precision Devices Surfometer 400 profilometer available at the University of Florida Major Analytical Instrumentation Center will be used to quantify the surface roughness. This instrument conducts a line scan across a surface and provides the root mean square roughness, Rrms, which represents the average deviation of the surface from an average perfectly flat surface. The vertical resolution of the profilometer is on the order of 0.01 microns, much less than the smallest bead size (0.1 μm). Five line scans will be run on each sample and the average roughness calculated. The direct shear test method will use 2-in mortar or grout cubes. The proposed method consists of casting two mortar cubes of standard size. One cube is then glued to a steel fixture. The adhesive test surface is then treated as required and adhered. The coverage area of adhesive can be varied as needed to ensure that the failure occurs at the test adhesive interface. The direct shear test will be used to measure the interfacial fracture energy. By correlating the measured fracture energy to the measured surface roughness and applying extrapolation techniques it will be possible to form a dependence curve of fracture energy vs surface roughness. Furthermore, this may prove valuable in quantifying the bond strength of FRP reinforced concrete members which failure is controlled by the strength of concrete-epoxy interface (members exposed to moist environments).
The goal of this project is to evaluate the effect of water leaks on the wind uplift resistance of wood roof systems, and on the performance of a spray-foam polyurethane retrofit. Studies have proven that spray-foam polyurethane adhesive provides both excellent insulation to roof and significant increase in the strength of the roof. However, current methods of installation may trap water at the wood sheathing to foam interface, which can have damaging effects on the materials. This investigation will monitor the wood moisture content, water leakage and the interior and exterior humidity and temperature conditions for four roof attic systems. The attics, which will be built this Spring, will be exposed to real and simulated rainfall and weather conditions for about 9 months. During the course of this long-term exposure, the data will uploaded to the internet for dissemination purposes and analysis. The REU student will be introduced to the structural systems used in traditional residential construction and to the sustainable retrofit options that are available to mitigate future hurricane damage. The student will participate in the construction of test specimens, and be trained to document the ambient and materials conditions of wood structural materials, and to perform structural and material testing on wood samples and foam samples, to determine properties and changes occurring over time.
There has been tremendous interest recently in sustainable and energy efficient construction techniques, spurred by federal policy to reduce carbon footprint and the enormous inefficient energy usage in buildings. One aspect that has garnered attention is the benefits provided by green (or vegetated) roof systems – they reduce the heat-island effects, slows storm run-off and they provide relatively cheap insulation of the building structures. The majority of these systems in the U.S. are located in the mid-west and west coasts, where they normally do not see hurricane wind speeds or extreme rainfall conditions. Currently there is no test method available to determine how green roofs may perform in hurricanes, and as such there is pent-up demand for green roofs in Florida and other hurricane-prone states, but no reliable means of evaluating system performance. Further, green roof plant materials for hot-humid climate regions have not been fully explored. The Prevatt research group is undertaking a study to determine realistic test method for evaluating the performance of vegetated roof systems in high winds and hurricanes. The REU student will construct full-scale plots of green roof systems and subject it to simulated hurricane wind speeds (up to 120 mph) to evaluate performance for the plantings, the media and roof module systems. The student will develop a hypothesis for the research, develop a test matrix, and schedule for the tests. The student will learn techniques for performing and interpreting these experiments, and will gain an introduction to the wind engineering concepts for predicting loads on buildings.