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Title: PROCESSING, OPTIMIZATION AND CHARACTERIZATION OF FIRE RETARDANT POLYMER NANOCOMPOSITES.
Creator: Zhuge, Jinfeng, Gou, Jihua, University of Central Florida
Abstract / Description: Fiber reinforced polymeric composites (FRPC) have superior physical and mechanical properties, such as high specific strength, light weight, and good fatigue and corrosion resistance. They have become competitive engineering materials to replace conventional metallic materials in many important sectors of industry such as aircraft, naval constructions, ships, buildings, transportation, electrical and electronics components, and offshore structures. However, since FRPC contain polymer matrix,...
Show moreFiber reinforced polymeric composites (FRPC) have superior physical and mechanical properties, such as high specific strength, light weight, and good fatigue and corrosion resistance. They have become competitive engineering materials to replace conventional metallic materials in many important sectors of industry such as aircraft, naval constructions, ships, buildings, transportation, electrical and electronics components, and offshore structures. However, since FRPC contain polymer matrix, the polymer composites and their structures are combustible. FRPC will degrade, decompose, and sometimes yield toxic gases at high temperature or subject to fire conditions. The objective of this study is to design and optimize fire retardant nanopaper by utilizing the synergistic effects of different nanoparticles. A paper-making technique that combined carbon nanofiber, nanoclay, polyhedral oligomeric silsesquioxanes, graphite nanoplatelet, and ammonium polyphosphate into self-standing nanopaper was developed. The fire retardant nanopaper was further incorporated into the polymer matrix, in conjunction with continuous fiber mats, through resin transfer molding process to improve fire retardant performance of structural composites. The morphology, thermal stability, and flammability of polymer composites coated with hybrid nanopaper were studied. The cone calorimeter test results indicated that the peak heat release rate of the composites coated with a CNF-clay nanopaper was reduced by 60.5%. The compact char material formed on the surface of the residues of the CNF-clay nanopaper was analyzed to understand the fire retardant mechanism of the nanopaper. The financial support from Office of Naval Research is acklowdged.
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Date Issued: 2010
Identifier: CFE0003151, ucf:48618
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003151

Title: Pressure Image Based Attitude Controller for Small Unmanned Aerial Vehicles.
Creator: Thompson, Kenneth, Xu, Yunjun, Gou, Jihua, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: As technology improves, small unmanned aerial vehicles (SUAV) have been identified for their utility in a variety of applications in which larger unmanned craft may be incapable of accomplishing mission objectives. These aircraft with their small size and long flight durations are ideal for hazardous inspection and long duration surveillance missions. One challenge preventing the widespread adoption of these systems is their instability to abrupt changes in the flow field around them due to...
Show moreAs technology improves, small unmanned aerial vehicles (SUAV) have been identified for their utility in a variety of applications in which larger unmanned craft may be incapable of accomplishing mission objectives. These aircraft with their small size and long flight durations are ideal for hazardous inspection and long duration surveillance missions. One challenge preventing the widespread adoption of these systems is their instability to abrupt changes in the flow field around them due to wind gusts or flow separation.Currently, traditional rigid body based sensors are implemented in their flight control systems, which are sufficient in higher inertia aircraft for accurate control.However, in low inertia SUAV applications during a flow event, often, the inertial sensors are incapable of detecting the event before catastrophic failure.A method of directly measuring the flow information around the SUAV in order to generate control commands will improve the stability of these systems by allowing these systems to directly react to flow events.In contrast, established inertial based control systems can only react to changes in vehicle dynamics caused by flow events.Such a method is developed utilizing a network of pressure and shear sensors embedded in the wing and used to create (")flow images(") which can be easily manipulated to generate control commands.A method of accurately calculating the aerodynamic moment acting on the aircraft based on the flow image is also developed for implementation of flow image-based control in real world systems.
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Date Issued: 2018
Identifier: CFE0007417, ucf:52722
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007417

Title: NONDESTRUCTIVE TESTING METHODS AIDED VIA NUMERICAL COMPUTATION MODELS FOR VARIOUS CRITICAL AEROSPACE AND POWER GENERATION SYSTEMS.
Creator: Warren, Peter, Ghosh, Ranajay, Raghavan, Seetha, Gou, Jihua, University of Central Florida
Abstract / Description: A current critical necessity for all industries which utilize various equipment that operates in hightemperature and extreme environments, is the ability to collect and analyze data via non destructivetesting (NDT) methods. Operational conditions and material health must be constantly monitoredif components are to be implemented precisely to increase the overall performance and efficiencyof the process. Currently in both aerospace and power generation systems there are many methodsthat are...
Show moreA current critical necessity for all industries which utilize various equipment that operates in hightemperature and extreme environments, is the ability to collect and analyze data via non destructivetesting (NDT) methods. Operational conditions and material health must be constantly monitoredif components are to be implemented precisely to increase the overall performance and efficiencyof the process. Currently in both aerospace and power generation systems there are many methodsthat are being employed to gather several necessary properties and parameters of a given system.This work will focus primarly on two of these NDT methods, with the ultimate goal of contributingto not only the method itself, but also the role of numerical computation to increase the resolutionof a given technique. Numerical computation can attribute knowledge onto the governing mechanicsof these NDT methods, many of which are currently being utilized in industry. An increase inthe accuracy of the data gathered from NDT methods will ultimately lead to an increase in operationalefficiency of a given system.The first method to be analyzed is a non destructive emmision technique widely referred to asaccoustic ultrasonic thermography. This work will investigate the mechanism of heat generationin acoustic thermography using a combination of numerical computational analysis and physicalexperimentation. Many of the challenges typical of this type of system are addressed in this work.The principal challenges among them are crack detection threshold, signature quality and the effectof defect interactions. Experiments and finite element based numerical simulations are employed,in order to evaluate the proposed method, as well as draw conclusions on the viability for futureextension and integration with other digital technologies for health monitoring. A method to determinethe magnitude of the different sources of heat generation during an acoustic excitation isalso achieved in this work. Defects formed through industrial operation as well as defects formedthrough artificial manufacturing methods were analyzed and compared.The second method is a photoluminescence piezospectroscopic (PLPS) for composite materials.The composite studied in this work has one host material which does not illuminate or have photoluminescenceproperties, the second material provides the luminescence properties, as well asadditional overall strength to the composite material. Understanding load transfer between the reinforcementsand matrix materials that constitute these composites hold the key to elucidating theirmechanical properties and consequent behavior in operation. Finite element simulations of loadingeffects on representative embedded alumina particles in a matrix were investigated and comparedwith experimental results. The alumina particles were doped with chromium in order to achieveluminscence capability, and therefore take advantage of the piezospectrscopic measurement technique.Mechanical loading effects on alumina nanoparticle composites can be captured with Photostimulated luminescent spectroscopy, where spectral shifts from the particles are monitored withload. The resulting piezospectroscopic (PS) coefficients are then used to calculate load transferbetween the matrix and particle. The results from the simulation and experiments are shown tobe in general agreement of increase in load transferred with increasing particle volume fractiondue to contact stresses that are dominant at these higher volume fractions. Results from this workpresent a combination of analytical and experimental insight into the effect of particle volume fractionon load transfer in ceramic composites that can serve to determine properties and eventuallyoptimize various parameters such as particle shape, size and dispersion that govern the design ofthese composites prior to manufacture and testing.
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Date Issued: 2018
Identifier: CFE0007262, ucf:52203
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007262

Title: Printable Carbon Nanotube Based Multifunctional Nanocomposites for Strain Sensing and Self-heating.
Creator: Wang, Xin, Gou, Jihua, Challapalli, Suryanarayana, Xu, Yunjun, University of Central Florida
Abstract / Description: The unique properties of carbon nanotubes (CNTs) represent a potential for developing a piezo-resistive strain sensor and a resistive heating sheet with a smart structure. Conventional fabrication techniques of CNT based nanocomposites such as molding, casting or spray coating lack the ability to control the geometry and properties of fabricated composites. In order to meet the various requirements of strain sensing or self-heating applications, nanocomposites with complex geometry and...
Show moreThe unique properties of carbon nanotubes (CNTs) represent a potential for developing a piezo-resistive strain sensor and a resistive heating sheet with a smart structure. Conventional fabrication techniques of CNT based nanocomposites such as molding, casting or spray coating lack the ability to control the geometry and properties of fabricated composites. In order to meet the various requirements of strain sensing or self-heating applications, nanocomposites with complex geometry and controllable properties are in high demand. Digital printing technique is able to fabricate CNT films with precisely controlled geometry with the help of computer aided design, and their properties could also be controlled by adjusting the printing parameters. The objective of this study is to investigate the printing-structure-property relationship of CNT based multifunctional nanocomposites fabricated by digitally controlled spray deposition process for strain sensing and self-heating. A spray deposition modeling (SDM) printer that uses a 12-array inkjet nozzle attached to an x-y plotter was developed for the fabrication of CNT layers. Most of previously-reported CNT based nanocomposite strain sensors only have limited stretchability and sensitivity for measuring diverse human motions. Additionally, strain sensors fabricated by traditional techniques are only capable of measuring strain in a single direction, but for monitoring human motion with complicated strain condition, strain sensors that can measure strain from multi-direction are favorable. In this dissertation, highly stretchable (in excess of 45% strain) and sensitive (gauge factor of 35.75) strain sensors with tunable strain gauge factors were fabricated by incorporating CNT layers into polymer substrate using SDM printing technique. The cyclic loading-unloading test results revealed that the composite strain sensors exhibited excellent long-term durability. Due to the flexibility of the printing technique, rosette-typed sensors were fabricated to monitor complicated human motions. These superior sensing capabilities of the fabricated nanocomposites offer potential applications in wearable strain sensors. Resistive heating properties of CNT based nanocomposites were also investigated. The electrically resistive heating of these composites can be a desirable stimulus to activate the shape memory effect of polymer matrix. CNT based nanocomposites fabricated by traditional techniques showed a slow heating rate and same shape recovery ratio at different locations in nanocomposites. However, from the practical applications like smart skin or smart tooling perspective, programmable shape recovery ratio at specified locations are desirable. In this dissertation, the CNT based nanocomposites with a fast heating rate and controllable maximum surface temperature were fabricated using SDM technique. The study on the shape memory effect of nanocomposites showed that their shape recoverability was approximately 100% taking 30s under a low voltage of 40V. It is worth noting that through programming the number of printed CNT layers at different locations, the shape recovery rate could be controlled and localized actuation with the desired recovery ratio was achieved. The high efficiency of heating coupling with wide adjustability of surface temperature and shape recovery ratio at specified locations make the fabricated nanocomposites a promising candidate for electrical actuation applications.
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Date Issued: 2017
Identifier: CFE0006819, ucf:52892
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006819

Title: Piezoresistive Behavior of Carbon Nanopaper Polymer Composites for Strain Sensing.
Creator: Beyrooti, Jayden, Kwok, Kawai, Gou, Jihua, Kauffman, Jeffrey L., University of Central Florida
Abstract / Description: Carbon nanopapers made of carbon nanotubes (CNTs) or carbon nanofibers (CNFs), possess unique electrical, thermal and mechanical properties and when integrated with a polymer matrix, can become a multifunctional composite capable of strain sensing and heat actuation. Smart structures such as these can be used in many applications including deployable space structures, human motion detection, and structural health monitoring as flexible, sensitive and stable strain sensors in addition to...
Show moreCarbon nanopapers made of carbon nanotubes (CNTs) or carbon nanofibers (CNFs), possess unique electrical, thermal and mechanical properties and when integrated with a polymer matrix, can become a multifunctional composite capable of strain sensing and heat actuation. Smart structures such as these can be used in many applications including deployable space structures, human motion detection, and structural health monitoring as flexible, sensitive and stable strain sensors in addition to providing electrical heat actuation for the shape memory effect in polymers. This study focuses on strain sensing capabilities by developing a numerical model to predict piezoresistive behavior. The piezoresistive effect is a change in resistivity of a conductive network when a deformation is applied. This allows strain to be determined by simply measuring the electrical resistance. An equivalent resistor network can be formed to represent the fiber network. The proposed 2D model generates randomly oriented fibers inside a unit cell, determines their intersection points, and creates a mesh of the network for finite element analysis. Electrical conductivity is found for the initial and deformed fiber states by determining the current through the network for a known voltage. A piezoresistivity experimental study is conducted to investigate the strain sensing abilities of this material and validate model results. This simple model provides an initial framework that can be developed in future work. Despite its 2D nature, the model captures the governing mechanisms of piezoresistivity to a certain extent.
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Date Issued: 2019
Identifier: CFE0007788, ucf:52353
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007788

Title: Controlled Bubble Dynamics Inside Micropillar Arrays.
Creator: Khalil Arya, Faraz, Peles, Yoav, Gou, Jihua, Kassab, Alain, Abdolvand, Reza, University of Central Florida
Abstract / Description: Bubble dynamics inside micro domains was manipulated and used to pump liquid. Micropillars were formed inside two 1.5 mm wide and 220 (&)#181;m high microchannels with a length of 23 mm. One microchannel had three arrays of micropillars with diameters of 40 (&)#181;m and the other had a single array of micropillars with diameters of 30 (&)#181;m. An array of five 200 (&)#181;m by 200 (&)#181;m heaters was deposited inside these micropillar arrays and was used to control bubble size and...
Show moreBubble dynamics inside micro domains was manipulated and used to pump liquid. Micropillars were formed inside two 1.5 mm wide and 220 (&)#181;m high microchannels with a length of 23 mm. One microchannel had three arrays of micropillars with diameters of 40 (&)#181;m and the other had a single array of micropillars with diameters of 30 (&)#181;m. An array of five 200 (&)#181;m by 200 (&)#181;m heaters was deposited inside these micropillar arrays and was used to control bubble size and trajectory. A sequential power switching of the heaters was used to pump liquid in a desired direction with a flow rate of up to 133 (&)#181;l/min for the three arrays micropillars microchannel and up to 44.4 (&)#181;l/min for the single array micropillars device.
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Date Issued: 2018
Identifier: CFE0007757, ucf:52381
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007757

Title: Shape Recovery Behavior of Carbon Nanopaper Shape Memory Polymer Composite.
Creator: Ozdemir, Veli Bugra, Kwok, Kawai, Gou, Jihua, Ghosh, Ranajay, University of Central Florida
Abstract / Description: This thesis presents analytical, experimental and modeling studies of the shape recovery behavior of electrically activated Carbon Nanopaper (CNP) Shape Memory Polymer (SMP)composite. The composite structure studied consists of a CNP layer sandwiched by two SMP layers where the CNP layer acts as a ?exible electrical heater when a voltage difference is applied. The behavior of CNP/SMP composite presents a coupled electrical - thermal - structural problem. The governing equations for the...
Show moreThis thesis presents analytical, experimental and modeling studies of the shape recovery behavior of electrically activated Carbon Nanopaper (CNP) Shape Memory Polymer (SMP)composite. The composite structure studied consists of a CNP layer sandwiched by two SMP layers where the CNP layer acts as a ?exible electrical heater when a voltage difference is applied. The behavior of CNP/SMP composite presents a coupled electrical - thermal - structural problem. The governing equations for the multiphysics behavior are derived. Derived parameters as a result of multiphysics analysis and effects of these parameters on the shape recovery behavior are investigated. The mechanical properties of the carbon nanopaper and viscoelastic properties of the shape memory polymer are characterized. A nonlinear, fully coupled electrical -thermal-structural ?nite element model is developed, and shape recovery experiments are carried out to validate multiphysics analysis and ?nite element model of the shape recovery of the CNP/SMP composite. Finite element model captures the general behavior of shape recovery, but overpredicts shape ?xity and shape recovery rate.
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Date Issued: 2019
Identifier: CFE0007700, ucf:52417
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007700

Title: Vision-Based Testbeds for Control System Applicaitons.
Creator: Sivilli, Robert, Xu, Yunjun, Gou, Jihua, Cho, Hyoung, Pham, Khanh, University of Central Florida
Abstract / Description: In the field of control systems, testbeds are a pivotal step in the validation and improvement of new algorithms for different applications. They provide a safe, controlled environment typically having a significantly lower cost of failure than the final application. Vision systems provide nonintrusive methods of measurement that can be easily implemented for various setups and applications. This work presents methods for modeling, removing distortion, calibrating, and rectifying single and...
Show moreIn the field of control systems, testbeds are a pivotal step in the validation and improvement of new algorithms for different applications. They provide a safe, controlled environment typically having a significantly lower cost of failure than the final application. Vision systems provide nonintrusive methods of measurement that can be easily implemented for various setups and applications. This work presents methods for modeling, removing distortion, calibrating, and rectifying single and two camera systems, as well as, two very different applications of vision-based control system testbeds: deflection control of shape memory polymers and trajectory planning for mobile robots. First, a testbed for the modeling and control of shape memory polymers (SMP) is designed. Red-green-blue (RGB) thresholding is used to assist in the webcam-based, 3D reconstruction of points of interest. A PID based controller is designed and shown to work with SMP samples, while state space models were identified from step input responses. Models were used to develop a linear quadratic regulator that is shown to work in simulation. Also, a simple to use graphical interface is designed for fast and simple testing of a series of samples. Second, a robot testbed is designed to test new trajectory planning algorithms. A template-based predictive search algorithm is investigated to process the images obtained through a low-cost webcam vision system, which is used to monitor the testbed environment. Also a user-friendly graphical interface is developed such that the functionalities of the webcam, robots, and optimizations are automated. The testbeds are used to demonstrate a wavefront-enhanced, B-spline augmented virtual motion camouflage algorithm for single or multiple robots to navigate through an obstacle dense and changing environment, while considering inter-vehicle conflicts, obstacle avoidance, nonlinear dynamics, and different constraints. In addition, it is expected that this testbed can be used to test different vehicle motion planning and control algorithms.
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Date Issued: 2012
Identifier: CFE0004601, ucf:49187
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004601

Title: Multi-Sensor Optimization of the Simultaneous Turning and Boring Operation.
Creator: Deane, Erick, Xu, Chengying, Gou, Jihua, Gordon, Ali, University of Central Florida
Abstract / Description: To remain competitive in today's demanding economy, there is an increasing demand for improved productivity and scrap reduction in manufacturing. Traditional manufacturing metal removal processes such as turning and boring are still one of the most used techniques for fabricating metal products. Although the essential metal removal process is the same, new advances in technology have led to improvements in the monitoring of the process allowing for reduction of power consumption, tool wear,...
Show moreTo remain competitive in today's demanding economy, there is an increasing demand for improved productivity and scrap reduction in manufacturing. Traditional manufacturing metal removal processes such as turning and boring are still one of the most used techniques for fabricating metal products. Although the essential metal removal process is the same, new advances in technology have led to improvements in the monitoring of the process allowing for reduction of power consumption, tool wear, and total cost of production. Replacing used CNC lathes from the 1980's in a manufacturing facility may prove costly, thus finding a method to modernize the lathes is vital.This research focuses on Phase I and II of a three phase research project where the final goal is to optimize the simultaneous turning and boring operation of a CNC Lathe. From the optimization results it will be possible to build an adaptive controller that will produce parts rapidly while minimizing tool wear and machinist interaction with the lathe. Phase I of the project was geared towards selecting the sensors that were to be used to monitor the operation and designing a program with an architecture that would allow for simultaneous data collection from the selected sensors at high sampling rates. Signals monitored during the operation included force, temperature, vibration, sound, acoustic emissions, power, and metalworking fluid flow rates. Phase II of this research is focused on using the Response Surface Method to build empirical models for various responses and to optimize the simultaneous cutting process. The simultaneous turning and boring process was defined by the four factors of spindle speed, feed rate, outer diameter depth of cut, and inner diameter depth of cut. A total of four sets of experiments were performed. The first set of experiments screened the experimental region toiiidetermine if the cutting parameters were feasible. The next three set s of designs of experiments used Central Composite Designs to build empirical models of each desired response in terms of the four factors and to optimize the process. Each design of experiments was compared with one another to validate that the results achieved were accurate within the experimental region.By using the Response Surface Method optimal machining parameter settings were achieved. The algorithm used to search for optimal process parameter settings was the desirability function. By applying the results from this research to the manufacturing facility, they will achieve reduction in power consumption, reduction in production time, and decrease in the total cost of each part.
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Date Issued: 2011
Identifier: CFE0004098, ucf:49087
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004098

Title: Enhancing CNT Composites with Raman Spectroscopy.
Creator: Freihofer, Gregory, Raghavan, Seetha, Gou, Jihua, Zhai, Lei, University of Central Florida
Abstract / Description: Carbon Nanotubes (CNTs) have been the subject of intense research for their potential to improve a variety of material properties when developed as nano-composites. This research aims to address the challenges that limit the ability to transfer the outstanding nano-scale properties of CNTs to bulk nano-composites through Raman characterization.These studies relate the vibrational modes to microstructural characterization of CNT composites including stress, interface behavior, and defects. The...
Show moreCarbon Nanotubes (CNTs) have been the subject of intense research for their potential to improve a variety of material properties when developed as nano-composites. This research aims to address the challenges that limit the ability to transfer the outstanding nano-scale properties of CNTs to bulk nano-composites through Raman characterization.These studies relate the vibrational modes to microstructural characterization of CNT composites including stress, interface behavior, and defects. The formulation of a new fitting procedure using the pseudo-Voigt function is presented and shown to minimizethe uncertainty of characteristics within the Raman G and D doublet. Methods for optimization of manufacturing processes using the Raman characterization are presentedfor selected applications in a polymer multiwalled nanotube (MWNT) composite andlaser-sintered ceramic-MWNT composite. In the first application, the evolution of theMWNT microstructure throughout a functionalization and processing of the polymer-MWNT composite was monitored using the G peak position and D/G intensity ratio.Processing parameters for laser sintering of the ceramic-MWNT composites were optimized by obtaining maximum downshift in stress sensitive G-band peak position, whilekeeping disorder sensitive D/G integrated intensity ratio to a minimum. Advanced Raman techniques, utilizing multiple wavelengths, were used to show that higher excitationenergies are less sensitive to double resonance Raman effects. This reduces their ininfluence and allows the microstructural strain in CNT composites to be probed more accurately. The use of these techniques could be applied to optimize any processing parameters in the manufacturing of CNT composites to achieve enhanced properties.
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Date Issued: 2011
Identifier: CFE0004110, ucf:49098
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004110

Title: The Effect of Magnetic Bearing on the Vibration and Friction of a Wind Turbine.
Creator: Vorwaller, Mark, Lin, Kuo-Chi, Raghavan, Seetha, Gou, Jihua, University of Central Florida
Abstract / Description: Demands for sustainable energy have resulted in increased interest in wind turbines. Thus, despite widespread economic difficulties, global installed wind power increased by over 20% in 2011 alone. Recently, magnetic bearing technology has been proposed to improve wind turbine performance by mitigating vibration and reducing frictional losses. While magnetic bearing has been shown to reduce friction in other applications, little data has been presented to establish its effect on vibration and...
Show moreDemands for sustainable energy have resulted in increased interest in wind turbines. Thus, despite widespread economic difficulties, global installed wind power increased by over 20% in 2011 alone. Recently, magnetic bearing technology has been proposed to improve wind turbine performance by mitigating vibration and reducing frictional losses. While magnetic bearing has been shown to reduce friction in other applications, little data has been presented to establish its effect on vibration and friction in wind turbines. Accordingly, this study provides a functional method for experimentally evaluating the effect of a magnetic bearing on the vibration and efficiency characteristics of a wind turbine, along with associated results and conclusions.The magnetic bearing under examination is a passive, concentric ring design. Vibration levels, dominant frequency components, and efficiency results are reported for the bearing as tested in two systems: a precision test fixture, and a small commercially available wind turbine. Data is also presented for a geometrically equivalent ball bearing, providing a benchmark for the magnetic bearing's performance. The magnetic bearing is conclusively shown to reduce frictional losses as predicted by the original hypothesis. However, while reducing vibration in the precision test fixture, the magnetic bearing demonstrates increased vibration in the small wind turbine. This is explained in terms of the stiffness and damping of the passive test bearing. Thus, magnetic bearing technology promises to improve wind turbine performance, provided that application specific stiffness and damping characteristics are considered in the bearing design.
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Date Issued: 2012
Identifier: CFE0004452, ucf:49326
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004452

Title: experimental and numerical investigations on bond durability of cfrp strengthened concrete members subjected to environmental exposure.
Creator: Al-Jelawy, Haider, Mackie, Kevin, Gou, Jihua, Chopra, Manoj, University of Central Florida
Abstract / Description: Fiber reinforced polymer (FRP) composites have become an attractive alternative to conventional methods for external-strengthening of civil infrastructure, particularly as applied to flexural strengthening of reinforced concrete (RC) members. However, durability of the bond between FRP composite and concrete has shown degradation under some aggressive environments. Although numerous studies have been conducted on concrete members strengthened with FRP composites, most of those studies have...
Show moreFiber reinforced polymer (FRP) composites have become an attractive alternative to conventional methods for external-strengthening of civil infrastructure, particularly as applied to flexural strengthening of reinforced concrete (RC) members. However, durability of the bond between FRP composite and concrete has shown degradation under some aggressive environments. Although numerous studies have been conducted on concrete members strengthened with FRP composites, most of those studies have focused on the degradation of FRP material itself, relatively few on bond behavior under repeated mechanical and environmental loading.This thesis investigates bond durability under accelerated environmental conditioning of two FRP systems commonly employed in civil infrastructure strengthening: epoxy and polyurethane systems. Five environments were considered under three different conditioning durations (3 months, 6 months, and 1 year). For each conditioning environment and duration (including controls), the following were laboratory tested: concrete cylinders, FRP tensile coupons, and FRP-strengthened concrete flexural members. Numerical investigations were performed using MSC MARC finite element software package to support the outcomes of durability experimental tests. Precise numerical studies need an accurate model for the bond between FRP and concrete, a linear brittle model is proposed in this work that is calibrated based on nonlinear regression of existing experimental lap shear data.Results of tensile tests on FRP coupons indicate that both epoxy and polyurethane FRP systems do not degrade significantly under environmental exposure. However, flexural tests on the FRP strengthened concrete beams indicate that bond between FRP and concrete shows significant degradation, especially for aqueous exposure. Moreover, a protective coating suppresses the measured degradation. Also, experimental load-displacement curves for control beams show excellent agreement with numerical load-displacement curves obtained using the proposed bond model. Finally, a bond-slip model is predicted for concrete leachate conditioned beams by matching load-displacement curves for those beams with numerical load-displacement curves.
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Date Issued: 2013
Identifier: CFE0004971, ucf:49589
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004971

Title: Failure Analysis of Impact-Damaged Metallic Poles Repaired With Fiber Reinforced Polymer Composites.
Creator: Slade, Robert, Mackie, Kevin, Yun, Hae-Bum, Gou, Jihua, University of Central Florida
Abstract / Description: Metallic utility poles, light poles, and mast arms are intermittently damaged by vehicle collision. In many cases the vehicular impact does not cause immediate failure of the structure, but induces localized damage that may result in failure under extreme service loadings or can promote degradation and corrosion within the damaged region. Replacement of these poles is costly and often involves prolonged lane closures, service interruption, and temporary loss of functionality. Therefore, an in...
Show moreMetallic utility poles, light poles, and mast arms are intermittently damaged by vehicle collision. In many cases the vehicular impact does not cause immediate failure of the structure, but induces localized damage that may result in failure under extreme service loadings or can promote degradation and corrosion within the damaged region. Replacement of these poles is costly and often involves prolonged lane closures, service interruption, and temporary loss of functionality. Therefore, an in situ repair of these structures is required.This thesis examines the failure modes of damaged metallic poles reinforced with externally-bonded fiber reinforced polymer (FRP) composites. Several FRP repair systems were selected for comparison, and a set of medium and full-scale tests were conducted to identify the critical failure modes. The material properties of each component of the repair were experimentally determined, and then combined into a numerical model capable of predicting global response.Four possible failure modes are discussed: yielding of the unreinforced substrate, tensile rupture of the FRP, compressive buckling of the FRP, and debonding of the FRP from the substrate. It was found that simple linear, bilinear, and trilinear stress-strain relationships accurately describe the response of the composite and substrate components, whereas a more complex bond-slip relationship is required to characterize debonding. These constitutive properties were then incorporated into MSC.Marc, a versatile nonlinear finite element program. The output of the FEM analysis showed good agreement with the results of the experimental bond-slip tests.
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Date Issued: 2012
Identifier: CFE0004262, ucf:49514
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004262

Title: Performance of Mechanical and Non-mechanical Connections to GFRP Components.
Creator: Dike, Nnadozie, Mackie, Kevin, Gou, Jihua, Chopra, Manoj, University of Central Florida
Abstract / Description: There are presently many solutions to dealing with aging or deteriorated structures. Depending on the state of the structure, it may need to be completely over-hauled, demolished and replaced, or only specific components may need rehabilitation. In the case of bridges, rehabilitation and maintenance of the decks are critical needs for infrastructure management. Viable rehabilitation options include replacement of decks with aluminum extrusions, hybrid composite and sandwich systems, precast...
Show moreThere are presently many solutions to dealing with aging or deteriorated structures. Depending on the state of the structure, it may need to be completely over-hauled, demolished and replaced, or only specific components may need rehabilitation. In the case of bridges, rehabilitation and maintenance of the decks are critical needs for infrastructure management. Viable rehabilitation options include replacement of decks with aluminum extrusions, hybrid composite and sandwich systems, precast reinforced concrete systems, or the use of pultruded fiber-reinforced polymer (FRP) shapes. Previous research using pultruded glass fiber-reinforced polymer (GFRP) decks, focused on behaviour under various strength and serviceability loading conditions. Failure modes observed were specific to delamination of the flexural cross sections, local crushing under loading pads, web buckling and lip separation. However certain failure mechanisms observed from in-situ installations differ from these laboratory results, including behaviour of the connectors or system of connection, as well as the effect of cyclic and torsional loads on the connection.This thesis investigates the role of mechanical and non-mechanical connectors in the composite action and failure mechanisms in a pultruded GFRP deck system. There are many interfaces including top panel to I-beam, deck panel to girder, and panel to panel, but this work focuses on investigating the top panel connection. This is achieved through comparative component level shear, uplift, and flexure testing to characterize failure and determine connector capacity. Additionally, a connection of this GFRP deck system to a concrete girder is investigated during the system-level test. Results show that an epoxy non-mechanical connection may be better than mechanical options in ensuring composite behaviour of the system.
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Date Issued: 2012
Identifier: CFE0004371, ucf:49413
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004371

Title: VARIABLE FLUID FLOW REGIMES ALTER ENDOTHELIAL ADHERENS JUNCTIONS AND TIGHT JUNCTIONS.
Creator: Ranadewa, Dilshan, Steward, Robert, Gou, Jihua, Mansy, Hansen, University of Central Florida
Abstract / Description: Variable blood flow regimes influence a range of cellular properties ranging from cell orientation, shape, and permeability: all of which are dependent on endothelial cell-cell junctions. In fact, cell-cell junctions have shown to be an integral part of vascular homeostasis through the endothelium by allowing intercellular signaling and passage control through tight junctions (TJs), adherens junctions (AJs), and gap junctions (GJs). It was our objective to determine the structural response of...
Show moreVariable blood flow regimes influence a range of cellular properties ranging from cell orientation, shape, and permeability: all of which are dependent on endothelial cell-cell junctions. In fact, cell-cell junctions have shown to be an integral part of vascular homeostasis through the endothelium by allowing intercellular signaling and passage control through tight junctions (TJs), adherens junctions (AJs), and gap junctions (GJs). It was our objective to determine the structural response of both AJs and TJs under steady and oscillatory flow. Human brain microvascular endothelial cells (HBMECs) were cultured in a parallel plate flow chamber and exposed to separate trails of steady and oscillatory fluid shear stress for 24 hours. Steady flow regimes consisted of a low laminar flow (LLF) of 1 dyne/cm2, and a high laminar flow (HLF) of 10 dyne/cm2 and oscillatory flow regimes consisted of low oscillatory flow (LOF) +/- 1 dyne/cm2 and high oscillatory flow (HLF) of +/- 10 dyne/cm2. We then imaged the TJs ZO-1 Claudin-5 and AJs JAM-A VE-Cadherin and subsequently analyzed their structural response as a function of pixel intensity. Our findings revealed an increase in pixel intensity between LLF and LOF along the boundary of the cells in both TJs ZO1 Claudin 5. Therefore, our results demonstrate the variable response of different cell-cell junctions under fluid shear, and for the first time, observes the difference in cell-cell junctional structure amongst steady and oscillatory flow regimes
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Date Issued: 2019
Identifier: CFE0007518, ucf:52618
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007518

Title: Decentralized Consensus-based Control Allocation For Some Dynamical Systems.
Creator: Mark, August, Xu, Yunjun, Gou, Jihua, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: In this dissertation, three separate studies, wherein techniques from graph theory and consensus control are used to address control allocation problems, are presented. In the first study, a decentralized allocator is presented for synthetic jet actuators and control surfaces onboard a small unmanned aerial vehicle to cooperatively generate desired aerodynamic moments. First order linear dynamics are assumed for both the synthetic jet actuators and control surfaces. A weighted consensus...
Show moreIn this dissertation, three separate studies, wherein techniques from graph theory and consensus control are used to address control allocation problems, are presented. In the first study, a decentralized allocator is presented for synthetic jet actuators and control surfaces onboard a small unmanned aerial vehicle to cooperatively generate desired aerodynamic moments. First order linear dynamics are assumed for both the synthetic jet actuators and control surfaces. A weighted consensus algorithm with limited feedback is used for the aerodynamic moment contribution allocator considering constraints. In the second study, the same allocation problem as in the first study is considered, but the actuator dynamics are now assumed to behave according to second order nonlinear dynamics. In the third study, a spray allocator is presented for an array of nozzles used to cool a large heated surface in order to address the local disagreement in surface temperature within sprayed sections. Within each study, the stability of each system is proven, and the performance of each allocator is demonstrated via simulations.
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Date Issued: 2019
Identifier: CFE0007496, ucf:52636
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007496

Title: Spray Deposition Modeling of Carbon Nano-Inks.
Creator: Sparkman, John, Gou, Jihua, Xu, Yunjun, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: Carbon nanopaper (CNP) exhibits qualities that are desirable for a number of applications such as flame retardancy, lightning protection, and flexible printed circuit boards. CNP has become a desired engineering material in many important sectors of industries such as space, automotive, aviation, and military. However the production of consistent thicknesses and dispersion remains a challenge for practical use. Most of the standard methods of production do not allow for continuous...
Show moreCarbon nanopaper (CNP) exhibits qualities that are desirable for a number of applications such as flame retardancy, lightning protection, and flexible printed circuit boards. CNP has become a desired engineering material in many important sectors of industries such as space, automotive, aviation, and military. However the production of consistent thicknesses and dispersion remains a challenge for practical use. Most of the standard methods of production do not allow for continuous applications or digital fabrication of the CNP. In this work, CNP is produced two different ways that allows for continuous production and digital fabrication. The continuous CNP making technique uses vacuum infiltration along with air atomization and a continuous drive belt system to produce a continuous roll of the CNP. This system is able to produce an 11 (&)#181;m (&)#177; 2 (&)#181;m CNP at 6 inches per min with an electrical resistivity of 59 ? per square. The major advantage of this production process is the ability to mass manufacture the CNP. Spray deposition modeling (SDM) is a digital fabrication process that uses a 12 array bubble jet nozzle attached to a digital control x-y plotter combined with a heated substrate which induces evaporation. This process is able to produce paper with variable thicknesses in defined locations. The maximum thickness of the CNP produced is 10 (&)#181;m with a resistivity of 95.7 ? per square. A strong advantage of this CNP production method comes from the ability to digitally print images. The controllable thickness and selective location printing presents an effective alternative to costlier methods and provides a solution to many geometrical CNP issues.
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Date Issued: 2015
Identifier: CFE0006231, ucf:51073
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006231

Title: Development of 3D Vision Testbed for Shape Memory Polymer Structure Applications.
Creator: Thompson, Kenneth, Xu, Yunjun, Gou, Jihua, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: As applications for shape memory polymers (SMPs) become more advanced, it is necessary to have the ability to monitor both the actuation and thermal properties of structures made of such materials. In this paper, a method of using three stereo pairs of webcams and a single thermal camera is studied for the purposes of both tracking three dimensional motion of shape memory polymers, as well as the temperature of points of interest within the SMP structure. The method used includes a stereo...
Show moreAs applications for shape memory polymers (SMPs) become more advanced, it is necessary to have the ability to monitor both the actuation and thermal properties of structures made of such materials. In this paper, a method of using three stereo pairs of webcams and a single thermal camera is studied for the purposes of both tracking three dimensional motion of shape memory polymers, as well as the temperature of points of interest within the SMP structure. The method used includes a stereo camera calibration with integrated local minimum tracking algorithms to locate points of interest on the material and measure their temperature through interpolation techniques. The importance of the proposed method is that it allows a means to cost effectively monitor the surface temperature of a shape memory polymer structure without having to place intrusive sensors on the samples, which would limit the performance of the shape memory effect. The ability to monitor the surface temperatures of a SMP structure allows for more complex configurations to be created while increasing the performance and durability of the material. Additionally, as compared to the previous version, both the functionalities of the testbed and the user interface have been significantly improved.
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Date Issued: 2015
Identifier: CFE0005893, ucf:50860
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005893

Title: Deposition Thickness Modeling and Parameter Identification for Spray Assisted Vacuum Filtration Process in Additive Manufacturing.
Creator: Mark, August, Xu, Yunjun, Gou, Jihua, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: To enhance mechanical and/or electrical properties of composite materials used in additive manufacturing, nanoparticles are often time deposited to form nanocomposite layers. To customize the mechanical and/or electrical properties, the thickness of such nanocomposite layers must be precisely controlled. A thickness model of filter cakes created through a spray assisted vacuum filtration is presented in this paper, to enable the development of advanced thickness controllers. The mass transfer...
Show moreTo enhance mechanical and/or electrical properties of composite materials used in additive manufacturing, nanoparticles are often time deposited to form nanocomposite layers. To customize the mechanical and/or electrical properties, the thickness of such nanocomposite layers must be precisely controlled. A thickness model of filter cakes created through a spray assisted vacuum filtration is presented in this paper, to enable the development of advanced thickness controllers. The mass transfer dynamics in the spray atomization and vacuum filtration are studied for the mass of solid particles and mass of water in differential areas, and then the thickness of a filter cake is derived. A two-loop nonlinear constrained optimization approach is used to identify the unknown parameters in the model. Experiments involving depositing carbon nanofibers in a sheet of paper are used to measure the ability of the model to mimic the filtration process.
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Date Issued: 2015
Identifier: CFE0005974, ucf:50788
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005974

Title: High Temperature Mechanics of Aerospace Ceramic Composites Characterized via Synchrotron Radiation.
Creator: Manero, Albert, Raghavan, Seetha, Kauffman, Jeffrey L., Gou, Jihua, University of Central Florida
Abstract / Description: This research investigates the mechanics of complex aerospace material systems designed for extreme environments. Ceramics and ceramic matrix composites (CMCs) provide highly sought-after capabilities including the potential to withstand extreme temperatures and heat fluxes, severe oxidation and mechanical stresses. Two important material systems form the basis of the scope for this effort: i) thermal barrier coatings (TBCs) on Ni-superalloys that have enabled dramatic increases in turbine...
Show moreThis research investigates the mechanics of complex aerospace material systems designed for extreme environments. Ceramics and ceramic matrix composites (CMCs) provide highly sought-after capabilities including the potential to withstand extreme temperatures and heat fluxes, severe oxidation and mechanical stresses. Two important material systems form the basis of the scope for this effort: i) thermal barrier coatings (TBCs) on Ni-superalloys that have enabled dramatic increases in turbine inlet temperatures exceeding 1100(&)deg;C; and ii) ceramic matrix composites that have shown capability and promise for hypersonic applications beyond 1300(&)deg;C. Understanding the mechanical and material properties of these materials as they evolve with temperature and load requires in-situ measurements under realistic representative environments, and from these measurements life expectancy and failure mechanisms can be more completely elucidated.In this work, TBCs representative of typical jet engine turbine blade coatings, comprised of a Yttria-stabilized zirconia top coat and NiCoCrAlY bond coat deposited on an IN 100 superalloy substrate were studied. Particular interest was given to the thermally grown oxide (TGO) that develops between the top layer and the bond coat that has a major influence on TBC durability. The oxide scale's development is linked to the typical failure mechanisms observed in application for aircraft engines, and the influence of internal cooling has been shown to vary the behavior and evolution over its lifetime. Tubular specimens coated via electron beam physical vapor deposition (EB-PVD) were investigated with hard synchrotron X-rays at Argonne National Laboratory's Advanced Photon Source, while subjected to realistic mechanical and thermal loading representative of the engine environment. A multi-variable investigation was conducted to determine the influence and magnitude of internal flow cooling, external applied force loading, and thermal exposure in cyclical application. The superposition of all these variables together creates variation spatially across in service turbine blades. Lattice strains for the axial and radial directions were resolved for the YSZ top coat layer and the internal thermally grown oxide scale. The findings revealed that during sufficiently high axial loading the strain condition for both the thermally grown oxide and top coat layers may be reversed in direction, and demonstrated how the internal flow and applied mechanical loading produce opposing effects while showing the magnitude of each variable. This reversal of the strain direction is known to contribute to the failure mechanics in the system. This discovery shows that with increased internal cooling to critical zones that experience higher mechanical loads, it is possible to tune the response of the system and prevent the reversal from compressive to tensile strains (in the axial direction). The impact of the results has the potential to be used in design for enhanced durability of the multi-layer coatings.Ceramic matrix composites are identified to comprise the next generation of turbine blades and high temperature parts. All oxide ceramic matrix composites were investigated for the influence of micro-structure variations and processing on the mechanics of the system. Isolation techniques of the all alumina composite by means of synchrotron diffraction and tomography presented a novel non-destructive method for evaluating the constituent's properties and evolution. The study successfully revealed how variations in grain size and elastic modulus result in a complex strain states. Further tomographical analysis identified system mechanics influenced by porosity and processing effects. CMCs with an yttria based environmental barrier coating were investigated for comparison to uncoated parts to further capture the in service condition, and revealed considerations for how to improve the durability of the inter-laminar strength of environmental barrier coatings interface. Together the research conducted has contributed to the high temperature aerospace materials' community, and the experimental work taken strides to provide validation and support future numerical simulation for developing better lifetime modeling. Resulting high temperature mechanics' information has the potential to enhance the design of aerospace components for substantial increases in durability. The outcomes from this work can be leveraged to continue advancing material characterization for aerospace material systems under complex and extreme environments.
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Date Issued: 2016
Identifier: CFE0006836, ucf:51794
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006836

bond (3)	+ -
nanocomposites (3)	+ -
piezospectroscopy (3)	+ -
Basalt Fiber (2)	+ -
Finite Element Analysis (2)	+ -

Shape Memory Polymer (2)	+ -
TBC (2)	+ -
Testbed (2)	+ -
XRD (2)	+ -
biaxial stress (2)	+ -
carbon nanopaper (2)	+ -
composite (2)	+ -
deck (2)	+ -
shape memory polymer (2)	+ -
synchrotron (2)	+ -
ASTM D4812 (1)	+ -
ASTM D6671 (1)	+ -
Accelerated bridge construction (1)	+ -
Acoustic Thermography (1)	+ -
Acropora cervicornis (1)	+ -
Aerodynamics (1)	+ -
All-strain Based Modified-Mohr-Coulomb Fracture Model (1)	+ -
Alumina reinforcement (1)	+ -
Aluminium magnesium boride (1)	+ -
Anisotropic Fracture (1)	+ -
Anisotropic plasticity (1)	+ -
BUBBLE DYNAMICS (1)	+ -
Bond-Slip (1)	+ -
Buckypaper (1)	+ -
CMC (1)	+ -

Gou, Jihua (47)	+ -
University of Central Florida (47)	+ -
Raghavan, Seetha (14)	+ -
Xu, Yunjun (10)	+ -
Bai, Yuanli (9)	+ -

Lin, Kuo-Chi (9)	+ -
Mackie, Kevin (6)	+ -
Orlovskaya, Nina (6)	+ -
Chopra, Manoj (4)	+ -
Gordon, Ali (4)	+ -
Challapalli, Suryanarayana (3)	+ -
Kapat, Jayanta (3)	+ -
Kassab, Alain (3)	+ -
Kwok, Kawai (3)	+ -
Zhai, Lei (3)	+ -
Al-Jelawy, Haider (2)	+ -
An, Linan (2)	+ -
Blair, Richard (2)	+ -
Chen, Ruey-Hung (2)	+ -
Freihofer, Gregory (2)	+ -
Ghosh, Ranajay (2)	+ -
Kauffman, Jeffrey L. (2)	+ -
Makris, Nicos (2)	+ -
Manero, Albert (2)	+ -
Mark, August (2)	+ -
Thompson, Kenneth (2)	+ -
Wang, Xin (2)	+ -
Xie, Zhilin (2)	+ -
Xu, Chengying (2)	+ -
Zhuge, Jinfeng (2)	+ -

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