This thesis proposes a methodology for structural health monitoring that incorporates the inherent multi-functionality of carbon fibers. The hypothesis of the thesis is that by monitoring the electrical resistance of composite panels it is possible to detect impacts and statistically model their effects on the remaining useful service life of structures. The proposed research investigates the application of statistics-based analysis to the measured electrical resistance signals during loading. The research also investigates the use of electrical resistance as a stress sensor by monitoring the resistance of test samples under tensile loading. / A Thesis submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester, 2012. / March 29, 2012. / Includes bibliographical references. / Arda Vanli, Professor Directing Thesis; Okenwa Okoli, Committee Member; Richard Liang, Committee Member.

ABSTRACT Since there has been an increase in the price of petroleum, there has been an increased need for photovoltaic systems over the last two decades. An increased number of private citizens are attracted to photovoltaic (PV) power as a viable source of independent renewable energy. Presently there is a mandate to continually improve the performance of the PV panels to maintain sustainability and to develop next generation PV systems. Most PV manufacturers state specifications of PV panels in terms of standard testing condition (STC) of 25º C or 77º F. However, many panels are operated in environments where temperatures are well above the level of STC reaching as high as 180º F (76º C). This has been shown to reduce the solar panel energy conversion, particularly the power output of the panels. To date literature has shown that the use of two cooling methods, water and ambient air to remove heat from the panels has proven minimally effective. This research proposes a method of heat reduction employing a recuperative nanofluid heat transfer system. The system employs a labyrinth of nanofluid filled tubes along the back of the PV panel. Through a field experiment, four combinations of a copper nanofluid combinations acting as a heat transfer medium were employed to remove the excess heat incident on four experimental units. The removal of heat from the solar panels to reservoirs simulating a domestic or industrial water heater simultaneously reduced the temperature of the panel to promote increased power output as well as water heating. The analysis of the data showed an average increase in reservoir temperature of 25º F. An analysis showed that the proposed system is more economical than either standard PV systems or the use of municipal utilities. The hope is that the proposed system will reduce the average citizen's energy cost by at least 30 percent as well as enable private citizens and some industries to operate independent of the utility grid. / A Dissertation submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester, 2012. / April 6, 2012. / Nanotechnology, Renwable Energy / Includes bibliographical references. / Joseph J. Pignatiello, Jr, Professor Directing Dissertation; Arda Vanli, Professor Co-Directing Dissertation; Rodney Roberts, University Representative; Mei Zhang, Committee Member.

The post synthetic assembly of nanowires into desired configurations presents a unique challenge. The inherent size of nanowires does not lend it self to a method or process capable of easily arranging or manipulating these materials. The recent understanding of how contact-line deposition, or the "coffee-ring effect", influences isotropic particles has lead to interest in investigating its influence over nanowires. Research has shown that nanowires can be aligned and selectively deposited at the edge of a drying droplet as a result of evaporation-induced capillary flow. From this basic understanding several methods have developed with the intent of producing a facile, robust, and scalable nanowire assembly process. This work provides insight into the coffee-ring effect and the mechanisms that draw from it to align, assemble, and pattern nanowire structures prior to introducing and providing the results of a new contact line deposition method. / A Thesis submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2011. / November 2, 2011. / Alignment, Evaporation-Induced, Nanowires, Patterning, Printing, Self-Assembly / Includes bibliographical references. / Mei Zhang, Professor Directing Thesis; Okenwa Okoli, Committee Member; Zhiyong Richard Liang, Committee Member.

Triboluminescent-based sensor systems have the potential to enable in-situ and distributed structural health monitoring of composite structures. Inability to effectively capture and transmit optical signals generated within opaque composites like concrete and carbon fiber reinforced polymers have however greatly limited their use. This problem has been solved by developing the bio-inspired in-situ triboluminescent optical fiber (ITOF) sensor. This sensor has the potential for wireless, in-situ, real-time and distributed (WIRD) damage monitoring. Its integrated sensing (triboluminescent thin film) and transmission (polymer optical fiber) components convert the energy from damage events like impacts and crack propagation into optical signals that are indicative of the magnitude of damage in composites. Utilizing the triboluminescent (TL) property of ZnS-Mn, the ITOF sensor has been successfully fabricated. Key design parameters were evaluated to develop a sensor with enhanced damage sensing capability. Sensor's performance was then characterized with Raman spectroscopy, field emission scanning electron microscopy (FESEM) and dynamic mechanical analysis (DMA). Flexural tests were also carried out to evaluate the damage sensing performance of the sensor before integrating into unreinforced concrete beams to create triboluminescent multifunctional cementitious composites (TMCC) with in-situ damage monitoring capabilities like biological systems. Results show that the ZnS-Mn in the epoxy coating of the ITOF sensor does not degrade the thermo-mechanical properties of the composite system. Raman spectroscopy indicates that the ZnS-Mn crystals retained their physical and chemical properties after undergoing the sensor fabrication process. Enhanced side-coupling of TL signals from the ITOF coating into the polymer optical fiber (POF) was achieved with TL thin film coating on POF. This makes distributed sensing possible when the length of the POF is coated with TL thin film. A new approach to damage characterization using TL emission profiles was employed with the TMCC. Three modes of sensor excitation in the TMCC were identified indicative of sensor's ability to sense crack propagation through the beam even when not in contact with the crack. FESEM analysis indicated that fracto-triboluminescence was responsible for the TL signals observed at beam failure. The TL profile analysis promises to facilitate better understanding of crack propagation in composite structural materials. / A Dissertation submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2013. / November 28, 2012. / bridges, composites, concrete, sensor, SHM, triboluminescence / Includes bibliographical references. / Okenwa I. Okoli, Professor Directing Dissertation; John O. Sobanjo, University Representative; Tao Liu, Committee Member; Zhiyong Liang, Committee Member.

Carbon nanotubes (CNTs) possess exceptional electrical properties. Networks of densely packed nanotubes that are formed by intercontacted or interconnected nanotubes and bundles were observed to form electrically conducting pathways over macroscopic dimensions and can be used for fabricating electronic devices and multifunctional composites. However, the electrical conductivity of these macroscopic networks is much less than the individual CNT's performance, primarily due to the large contact resistance between nanotubes. Many factors contribute to the contact resistance, and the majority of these factors are difficult to directly measure and control due to nanoscale dimensions. The approach of physics-based simulation would help to understand the dominating factors of carbon nanotube networks (CNNs) conductivity. In this thesis work, experimental characterization of the nanostructures and electrical properties of CNNs were carried out, and an equivalent electrical circuit model of CNNs was improved to study the electrical conduction mechanism and properties. To systematically investigate the structure-property relationship between the conductivity of CNNs and their nanostructures, microscopic images of CNNs were characterized with image analysis software to obtain the CNT rope length and diameter distributions. Volume fractions of CNTs in these CNNs were also determined by experimental measurements and literature reported density of CNTs. Raman spectroscopy results were used to characterize the alignment degree of magnetically aligned CNNs. The electrical properties of CNNs, including electrical conductivity and current-carrying capacity tests, were carried out. The conductivities of various types of CNNs were obtained, including single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs), and carbon nanofibers (CNF). CNNs of pure SWNTs possess the highest conductivity among all the networks studied. Another important electrical property, the current-carrying capacity, was also studied to understand the breakdown mechanism of CNNs. The tests were conducted to characterize the breakdown temperature and current density of the CNNs. It was determined that the breakdown of CNNs under high current stimuli was due to Joule heating. The modified electrical conductivity model is an electrical circuit simulation approach that reflects multiscale electrical conduction mechanisms and statistical nature of the CNNs. The model begins with nanoscale factors such as nanotube chirality and contact type, and then incorporates microscale factors such as dispersion and nanotube orientation, and further uses circuit computation simulation to calculate the bulk conductivity of the CNNs. Case studies were conducted to first validate the model and then reveal the structure-property relationships of different types of CNNs, including the effects of CNT orientation and chirality on the conductivity of the CNNs. The experimental results and developed model can be used to design and optimize CNNs for electrical applications. / A Thesis submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2009. / September 11, 2009. / Includes bibliographical references. / Richard Liang, Professor Directing Thesis; Petru Andrei, Committee Member; Ben Wang, Committee Member.

Many researchers regard carbon nanotube backlight units (CNT-BLUs) as a potential candidate for the liquid crystal display (LCD) industry. CNT buckypapers were tested as surface luminary sources for CNT-BLU applications. The field emission properties, durability and repeatability of a single-walled Carbon nanotube (SWCNT) buckypaper was studied for developing CNT-BLU. This study reports a laser irradiation process to enhance the field emission properties of buckypaper, which is a thin sheet of high-loading carbon nanotube networks. A scanning laser treated selected regions of the buckypaper to activate CNT emitters. This post-process causes a decrease in turn-on field and increases in the field enhancement factor ( and #946;), luminance intensity and uniformity of buckypaper emitters. The phosphorescence luminance intensity and uniformity of buckypaper emitters were measured and characterized. These exellent properties and performance were achieved by adjusting machining parameters of laser power, laser lens motion speed, laser resolution. Design of Experiment (DOE) methodology provided a method to rapidly search the feasible laser parameter setting for processing buckypaper and improving field emission properties within fewer experimental runs. DOE results indicated the proper laser treatment power density was 0.9 W/cm2. Furthermore, the effects of the laser treated emitter density was investigated under the same laser power density as the DOE results. The CNT emitter's altitude, diameter and spacing were characterized through an optics analysis after laser treatment. The emitter spacing directly impacted emission results when the laser power and treatment time were fixed. The increasing emitter density gave rise to an enhanced field emission current and luminance. However, a continuous and excessive increase of emitter density with spacing reduction generated a screening effect. As a result, the extended screening effect from the smaller spacing eventually crippled the field emission effectiveness. From luminance intensity and uniformity of field emission, the optimal ratio of average emitter altitude to emitter spacing was 3.4. The high effective buckypaper is suggested to have a density of 50 50 emitters/cm2, which presents an effective field enhancement factor of 3721 and a moderated screening effect of 0.005. Proper laser treatment appears to be an effective post-treatment process for optimizing field emission and luminance performance for a buckypaper cold cathode. / A Dissertation submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2010. / December 11, 2009. / Includes bibliographical references. / Ben Wang, Professor Co-Directing Dissertation; Mei Zhang, Professor Co-Directing Dissertation; James S. Brooks, University Representative; Richard Liang, Committee Member; Chuck Zhang, Committee Member; O. Arda Vanli, Committee Member.

Advanced composites offer robust mechanical properties and are widely used for structural applications in the aerospace, marine, defense and transportation industries. However, the inhomogenous nature of composite materials leaves them susceptible to problematic failure; thus the development of a means for detecting failure is imperative. Damage occurs when a load is applied and a distortion of the solid material results in deformation. This process also results in straining of the material. Strain, however, is a physical result of work being performed on a solid material making energy the commonality among all failure mechanisms. This study investigated the feasibility of using Triboluminescent zinc-sulphide manganese (ZnS:Mn) phosphors concentrated in vinyl ester resin for damage monitoring of polymer composites under flexural loading. These particulates react to straining or fracturing by emitting light of varied luminous intensity and detecting the crack initiation presently leading to catastrophic failure(s). Unreinforced vinyl ester resins and fiber-reinforced composite beams incorporated 5 - 50 % wt. concentrations of TL fillers, and were subjected to three-point bend tests. The intent of flexural testing was to observe the transient response of triboluminescence (TL) in both two- and three-phase composite systems throughout the failure cycle of notched beams, while changing the geometric constraints. Results indicate TL crystals emit light at various intensities corresponding to crystal concentration, the notch-length and imminent matrix fracture. The fracturing or deformation energy was estimated by the method of J-integral with varied notch-lengths, where a lower threshold for excitation was found to be approximately <2 J/m^2, far below its critical fracture energy (~ 3 & 7 J/m^2). Consequently, concentrated samples showed nearly 50 % reductions of mechanical moduli due to high loading levels, which subsequently affected the Triboluminescent response. As a result, an optimal 6 % vol. of TL particulates was chosen for further study and exhibited significant signal-to-noise response. Scanning electron microscopy (SEM) revealed particulate inclusions with shearing bands and semblance of particle to resin adhesion, as well as, cases of micro-cracking in reinforced samples. Despite significant parasitic affect to mechanical properties, the luminescent properties of TL occur at rupture for unreinforced composites. The cases of TL concentrated reinforced composites show detection of localized matrix phenomenon which are related to the material response and incurring internal strain-energy prior to any catastrophic failure. This indicates that TL in composite systems has the potential to detect micro-failures (micro-cracks) related to the weak matrix component. The triboluminescent signal was simulated as a rate-dependent model considering the load profile of the composite beam is known. / A Dissertation submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2013. / April 4, 2013. / Composites, Damage Sensors, Intrinsic, Multifunctional Materials, Structural Health Monitoring, Triboluminescence / Includes bibliographical references. / Okenwa Okoli, Professor Directing Dissertation; Naresh Dalal, University Representative; Ted Liu, Committee Member; Richard Liang, Committee Member.

The focus of the dissertation is to find solutions to increase the through-thickness thermal conductivity of fiber-reinforced polymer matrix composites (PMC). The objective is to explore novel concepts and new approaches to improve the through-thickness thermal conductivity up to 30W/mK for PMCs. First, this research involves understanding the principles of thermal transport in composite and nanocomposite materials. Then the research proceeds to model and design high thermal conducting composites and develop fabrication processes and characterization methods for functioning prototype materials. PMCs are advantageous for their light-weight, excellent strength and high modulus properties. However, due to insulation nature of polymer resin matrices, their bulk composites demonstrate poor through-thickness thermal conductivity making it unsuitable for applications that undergo thermal loads requiring a means for adequate heat dissipation. The research has carried out four technical approaches to achieve high through-thickness thermal conductivity. 1. Conductive Resins: Increasing the thermal conductivity of the matrix would increase the bulk through-thickness thermal conductivity. Experiments have been done using conductive fillers such as metallic nanoparticles and carbon nanotubes. Results have shown increase in the thermal conductivity but with the disadvantage of increased matrix viscosity making the fabrication process difficult. The thermal conductivity increases, however, is not adequate to achieve the objective solely. 2. Stitch Method: This method applies a continuous conductive path by stitching or inserting high conducting materials such as metal wires, high conducting carbon fiber or high conducting carbon yarns in the through-thickness direction of the composites. Experimentally, this method has proven to show a 27 fold increase in the through-thickness thermal conductivity at low volume fraction percentage of 5% with copper wire and 3.5 fold increase using K-1100 carbon yarn. 3. Long MWNT: Long MWNTs should create a conductive microstructure between fiber layers in composites. Providing conductive links improve the thermal transport of phonons, long MWNTs should more effectively provide thermal transport between fiber layers. However, the experimental results have yet to yield any improvements in the thermal properties of the composites. 4. Buckypaper: The use of thin film of dense nanotube networks or buckypapers is to improve the thermal connections between fiber layers as an interlayer material. If the buckypaper can make multiple connections between fiber layers, the nanotube network can be used to facilitate thermal transportation. However, the use of buckypaper has shown to have a reduced thermal conductivity value than that of a composite without buckypaper. Buckypaper in the experiment create resin rich areas between layers. Modeling efforts were performed to understand thermal transport mechanism, find solutions and predictions to through-thickness thermal conductivity of the multiscale composites. Micromechanical models were used to predict thermal property values for conductive resins as well as nanoparticle/fiber multiscale composites. Results show that only a few models prove useful with close predictions to experimental data. On the other hand, finite element modeling (FEM), allows the exploration of the critical nanoparticle/fiber interactions and their effects on thermal properties of the resultant composites. The FEM results show that it is the interconnections between nanoparticle and fibers, rather than concentration of conductive fillers, significantly impact the through-thickness thermal conductivity in PMCs, where continuous thermal pathways were the most important for performance improvement. Discontinuous pathways of nanotubes and conducting materials showed very limited or no effects on thermal conductivity improvements. These results provide viable information for future design and fabrication of high through-thickness thermal conductivity composite materials for thermal management multifunctional applications. / A Dissertation submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester, 2009. / November 4, 2009. / Includes bibliographical references. / Zhiyong Richard Liang, Professor Co-Directing Dissertation; Ben Wang, Professor Co-Directing Dissertation; James Brooks, University Representative; Chun (Chuck) Zhang, Committee Member.

Materials with negative Poisson's ratio are referred to as auxetic materials. They are different from conventional materials in their deformation behavior when responding to external stresses. The cross-section of the materials widens in the lateral direction when being stretched in the longitudinal direction and becomes narrower when being compressed longitudinally. While a number of natural auxetic materials exist, most auxetic materials are synthetic. They show interesting properties and have potential in several important applications. Auxetic materials exhibit better mechanical properties than conventional materials such as enhanced indentation resistance, shear resistance, toughness, damping and energy absorption capacity, sound absorption, variable permeability and capability of producing complex curvature. These properties are beneficial in a wide range of applications including personal protective equipments, sound absorbers, packaging, smart filtration, drug delivery, tissue scaffolding, seat cushioning, etc. A wide range of auxetic materials has been synthesized. They include different polymers, metals, composites and ceramics. Among these, auxetic polyurethane (PU) foam is one of the most widely studied types of auxetic materials. Auxetic PU foams are usually fabricated by altering the microstructure of conventional foams and the unusual mechanical properties originate from the deformation characteristics of the microstructures. Three most important processing parameters in fabricating auxetic PU foam that dictate auxetic behavior are processing temperature, heating time and volumetric compression ratio. This study addresses several important issues in the manufacturing and characterization of auxetic PU foam. First, an improved automatic measuring technique has been developed to determine Poisson's ratio of auxetic PU foam. The technique involves development of a Matlab based image processing program. The second part of the study includes an experimental design approach to identify significant processing parameters followed by optimization of those processing parameters in fabrication of auxetic PU foam. A split-plot factorial design has been selected for screening purpose. Response Surface Methodology (RSM) has been utilized to optimize the processing parameters in fabrication of auxetic PU foam. Two different designs named Box-Behnken and I-optimal designs have been employed for this analysis. The results obtained by those designs exhibit that I-optimal design provides more accurate and realistic results than Box-Behnken design when experiments are performed in split-plot manner. Finally, a near stationary ridge system is obtained by optimization analysis. As a result a set of operating conditions are obtained that produces similar minimum Poisson's ratio in auxetic PU foam. / A Thesis submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester, 2014. / July 11, 2014. / Includes bibliographical references. / Changchun Zeng, Professor Directing Thesis; Zhiyong Liang, Committee Member; Arda Vanli, Committee Member.

Despite the attractive properties of advanced ceramics, they are not popular for structural applications even though they possess high strength. Their low fracture toughness and brittle fracture mode are unwelcome for high integrity structure. Moreover, they fail at loads far below their theoretical strengths due to their inherent flaws. These have led to the development of reinforcing strategies to help enhance the fracture resistance of ceramics. However, reported strengths value are still far below theoretical strength, most reinforced ceramics suffer trade-off between strength and toughness, and most present reinforcement methods are material specific. In this work, a generic method for reinforcing ceramic materials for the enhancement of fracture resistance is described. Continuous ductile ligaments oriented in two orthogonal directions and forming 2-D network grid reinforcement structure was employed. The method involves two major stages: fabrication of regular channels in 2-D in ceramic matrix to form the preform and infiltration of the preform with the required reinforcement. Two different materials: carbon fibers and soft metal alloys were used as sacrificial materials for fabricating the aligned 2-D regular channels in alumina matrix. After the porous preforms were formed, molten aluminum alloys were infiltrated into the channels by the application of mechanical pressure, and this completes the composite fabrication process. Mechanical tests show that some porous preforms having area fraction of 2.7 % exhibited 27 % higher flexural strength than the solid specimens despite the porosity contained and this has been attributed to the ability of the channels to reduce the population and distribution of cracks in the porous material. The reinforced composites were also subjected to mechanical tests which revealed 217.6 % enhancement in flexural strength for the 7.79 % Al 7075 alloy reinforced composite. This magnitude of property enhancement was achieved due to the confinement of the matrix in the loop of the reinforcement and the beneficial residual compressive stress generated as a result of the difference in coefficient of thermal expansion (CTE) of the alumina and aluminum. The residual compressive stress delays crack initiation and crack propagation in the alumina matrix. It also reduces the stress concentration factor in the matrix, leading to higher failure stress and higher fracture toughness. / A Dissertation submitted to the Department of Industrial Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2012. / February 17, 2012. / Composite, Fracture Strength, Fracture Toughness, Reinforcement, Residual Stress, Stress Cocentration / Includes bibliographical references. / Okenwa Okoli, Professor Directing Dissertation; Simone Peterson-Hruda, University Representative; Mei Zhang, Committee Member; Zhiyong Richard Liang, Committee Member.