Models governing stochasticity in various systems are typically calibrated from data, therefore are subject to statistical errors/uncertainties which can lead to inferior decision making. This thesis develops statistically and computationally efficient data-driven methods for problems in stochastic simulation and optimization to quantify and hedge impacts of these uncertainties. The first half of the thesis focuses on efficient methods for tackling input uncertainty which refers to the simulation output variability arising from the statistical noise in specifying the input models. Due to the convolution of the simulation noise and the input noise, existing bootstrap approaches consist of a two-layer sampling and typically require substantial simulation effort. Chapter 2 investigates a subsampling framework to reduce the required effort, by leveraging the form of the variance and its estimation error in terms of the data size and the sampling requirement in each layer. We show how the total required effort is reduced, and explicitly identify the procedural specifications in our framework that guarantee relative consistency in the estimation, and the corresponding optimal simulation budget allocations. In Chapter 3 we study an optimization-based approach to construct confidence intervals for simulation outputs under input uncertainty. This approach computes confidence bounds from simulation runs driven by probability weights defined on the data, which are obtained from solving optimization problems under suitably posited averaged divergence constraints. We illustrate how this approach offers benefits in computational efficiency and finite-sample performance compared to the bootstrap and the delta method. While resembling distributionally robust optimization, we explain the procedural design and develop tight statistical guarantees via a generalization of the empirical likelihood method. The second half develops uncertainty quantification techniques for certifying solution feasibility and optimality in data-driven optimization. Regarding optimality, Chapter 4 proposes a statistical method to estimate the optimality gap of a given solution for stochastic optimization as an assessment of the solution quality. Our approach is based on bootstrap aggregating, or bagging, resampled sample average approximation (SAA). We show how this approach leads to valid statistical confidence bounds for non-smooth optimization. We also demonstrate its statistical efficiency and stability that are especially desirable in limited-data situations. We present our theory that views SAA as a kernel in an infinite-order symmetric statistic. Regarding feasibility, Chapter 5 considers data-driven optimization under uncertain constraints, where solution feasibility is often ensured through a "safe" reformulation of the constraints, such that an obtained solution is guaranteed feasible for the oracle formulation with high confidence. Such approaches generally involve an implicit estimation of the whole feasible set that can scale rapidly with the problem dimension, in turn leading to over-conservative solutions. We investigate validation-based strategies to avoid set estimation by exploiting the intrinsic low dimensionality of the set of all possible solutions output from a given reformulation. We demonstrate how our obtained solutions satisfy statistical feasibility guarantees with light dimension dependence, and how they are asymptotically optimal and thus regarded as the least conservative with respect to the considered reformulation classes.

Single walled carbon nanotubes (SWNTs) have demonstrated exceptional mechanical, thermal and electrical properties, and are regarded as one of the most promising reinforcement materials for the next generation of high performance structural and multifunctional composites with tremendous application potentials. However, to date, most application attempts have been hindered by several technical roadblocks, such as poor dispersion and weak interfacial bonding. Functionalization of nanotubes was suggested to be an effective way to overcome these technical issues and then to realize the full potential of nanotubes as reinforcement materials. In this dissertation, several original functionalization methods were proposed, studied, analyzed and quantitatively compared. These functionalization methods included precision sectioning of nanotubes using an ultra-microtome, electron-beam irradiation, amino-group grafting, and epoxide group grafting. Short nanotubes with open-ends show rich chemistry, ballistic transportation properties and capability of good dispersion. However, current reported cutting methods are difficult to protect tube sidewalls from devastation and to achieve desired length control. This research has developed a technique to precisely section aligned SWNT membranes through ultra-microtome in order to produce short and open-end tubes. Aligned SWNT membranes were sectioned to 50nm and 200nm. The results of AFM characterization and length statistical analysis have found the measured lengths were centered at 87nm and 246nm, respectively. Raman and TEM characterization results confirmed the minimized damage to the sidewalls. The cut-SWNTs were applied to nanocomposites fabrications. Young's modulus and strength of the composite were improved by 20% and 7%, respectively, when using 0.5wt% cut-SWNTs. The SEM results also confirmed the improvement in dispersion. The enhanced tensile strength indicates that load-transfer was improved due to the enhanced interfacial bonding. This dissertation also proposed a unique covalent sidewall functionalization through epoxy-grafting. The characterizations of Raman, FT-IR and TEM have proved the successful grafting of epoxide-group to the carbon nanotubes. The SEM results of the epoxy-grafted SWNTs reinforced composite indicated that significant improvement of dispersion was achieved. Dynamic Raman tests also revealed the considerable enhancement in the interfacial bonding. The tensile strength of nanocomposites was enhanced 27.1% and Young's modulus 30% with only 0.5wt% loading of epoxy-grafted SWNTs. When composites were fabricated with 1wt% loading of epoxy-grafted SWNTs, the strength and Young's modulus were improved by 40.3% and 60%, respectively. These substantial improvements are among the highest in the reported literatures. Furthermore, this research also succeeded in grafting amino-group onto SWNT sidewalls through one-step diazotization. Improvements in both dispersion and interfacial bonding were achieved. Young's modulus and strength for the amino-functionalized SWNTs composites with 0.5wt% loading were enhanced by 25% and 21.9%, respectively. The electron beam irradiation on the thin SWNTs membrane was both experimentally and theoretically investigated. Experimental results suggested that there exists a critical dose of irradiation in acquiring a desirable cross-linkage, above which significant enhancement of the SWNT membranes properties can be acquired. The theoretic modeling indicates that the density of cross-linkage is a quadratic function of the irradiation dosages. The irradiation-induced inter-tube bridging significantly enhanced the Young's modulus and tensile strength of the SWNTs membrane by 2 folds and 6 folds, respectively. Electric conductivity was also increased more than 1 fold. Both mechanical and electric properties improvements make the irradiated SWNT membranes very promising in the versatile applications, including electronic device, energy storage, biomaterials, and nanocomposites. All the methods developed in the dissertation demonstrated effectiveness in improving dispersion and interfacial bonding, resulting in considerable improvements in composite mechanical properties. Modeling of functionalization provided in-depth understanding and offered reasonable explanations of SWNTs length distribution, as well as carbon nanostructure transformation upon electron-beam irradiation. Both experimental and theoretical investigations would facilitate full realization of the potential of nanotubes-reinforced nanocomposites. / 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, 2006. / October 25, 2006. / Nanocomposites, Surface Modification, Carbon Nanotubes, Functionalization, Precision Cutting, Amino-Grafting, Epoxy-Grafting, Electron-Beam Irradiation, Nanotube Membrane, Dispersion, Interfacial Bonding, Buckypaper / Includes bibliographical references. / Zhiyong Liang, Professor Co-Directing Dissertation; , Professor Co-Directing Dissertation; James Brooks, Outside Committee Member.

Environmental and economic problems caused by over-dependence on fossil fuels have increased the demand and request for green energy produced by alternative renewable sources. Producing electricity by using photovoltaic cells (also called solar cells) is a fast growing industry. There are two main ways to make photovoltaic cells more efficient. One method is to improve the materials design and the other is to optimize the output by installing the solar panels on a tracking base that follows the sun. This research employed the latter method. The main purpose of the thesis was to design and assemble of a dual-axis solar tracker with a view to assess the improvement in solar conversion efficiency. A comparative analysis was performed using three systems, i.e., Dual-Axis Tracking, Single-Axis Tracking and Stationary Modules. ¡®¡¯Design Expert 6.0¡± statistical software was used to process the design of experiment and to determine the effects of four chosen factors (Tracking or No Tracking, Type of Modules, Time of the Day, and Weather Condition). The results showed that the use of the Dual-Axis Tracking System produced 18% gain of power output, compared with a Single-Axis Tracking System. The gain of output power with the Dual-Axis Tracking System was much higher (53%) when compared with a stationary system inclined at 30¢ª to the horizontal. A benefit-cost analysis performed on the three systems showed that the unit cost of energy produced by the Dual-Axis Tracker is $0.53, which is reasonable, considering the state of the technology and the potential added benefit of any future amortization when employed on a large scale. / A Thesis Submitted to the Department of Industrial Engineering in Partial Fulfillment of the Requirements for the Degree of Master of Science. / Fall Semester, 2008. / November 07, 2008. / Active Solar Tracker / Includes bibliographical references. / Yaw A. Owusu, Professor Directing Thesis; Samuel A. Awoniyi, Committee Member; Egwu E. Kalu, Committee Member.

Since carbon nanotubes (CNTs) were first discovered in 1990, many researchers have been striving to learn more about their remarkable mechanical and physical properties. With these exceptional properties, CNTs are considered by researchers as an ultimate reinforcement material for composite applications. However, many reports indicate that nanotube/epoxy composites are weaker or only slightly stronger than neat epoxy resins. This has been found to be primarily due to a combination of several factors, namely poor tube dispersion, inadequate alignment and weak interfacial bonding. In this study we focused on improving mechanical properties of nanocomposites and nanotube/carbon fiber multiscale reinforcement composites by improving nanotube dispersion and alignment. In order to improve dispersion, it is necessary to quantify tube dispersion quality first. We proposed a quantitative method by using Differential Scanning Calorimeter (DSC) to quantify tube dispersion uniformity in tube/resin mixtures. The preliminary result shows that this method is able to characterize the dispersion quality numerically. The previous dispersion technique was also investigated and modified through the use of a Design of Experiment (DOE) to improve the tube dispersion quality in Epon 862 resin. Results indicate that the tensile modulus of 0.5wt% nanocomposites has 26.5% improvement over that of the neat resin. This improvement is four times higher than that of 0.5wt% nanocomposites made by the previous tube dispersion technique. This modified tube dispersion technique was also used to manufacture multiscale nanocomposites to enhance through-thickness properties. The results also demonstrate that with the addition of 0.12wt% single-walled nanotubes (SWNTs), the storage modulus, tensile modulus and tensile strength of multiscale nanocomposites have a 16.74%, 0.6% and 3.8% increase over that of conventional fiber-reinforced composites. In order to further improve the mechanical performance of nanocomposites and multiscale nanocomposites, studies were carried out to align nanotube and nanofiber in nanocomposites and multiscale nanocomposites using an 8.5T magnetic field. Even though a certain degree of tube alignment was observed by means of Raman spectroscopy, the obvious improvement of mechanical properties of aligned nanotube and nanofiber/resin nanocomposites was not obtained, due to low tube loading and high viscosity issues. However, the property improvement of aligned multiscale nanocomposites was observed. The short-beam shear (SBS) strength of 0.04wt% aligned SWNT multiscale nanocomposites showed a 13.05% increase over that of randomly oriented multiscale nanocomposites when the SWNTs were aligned along the through-thickness direction. The effect on the Tgs of nanocomposites when adding nanotubes was also investigated. / A Dissertation Submitted to the Department of Industrial Engineering in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy. / Spring Semester, 2007. / March 16, 2007. / Dispersion, Alignment, Multiscale Nanocomposites, Nanotubes / Includes bibliographical references. / Zhiyong Liang, Professor Directing Thesis; James Brooks, Outside Committee Member; Ben Wang, Committee Member; Chuck Zhang, Committee Member; Young-Bin Park, Committee Member.

Fiber-reinforced composites are becoming more popular due to their high strength to weight ratio, making them a suitable replacement for traditional metals for lightweight applications. However, for applications where electro-conductivity and thermo-conductivity are required, fiber-reinforced composites lack the necessary properties without adding parasitic components. As a result of extensive research, high performance carbon nanotube-reinforced composites are considered as one of the key solutions to this issue, with buckypapers serving as the central constituent. Buckypapers are thin membranes of well-dispersed networks of nanotubes held together by van der Waals forces. Buckypapers are considered as one of the promising candidates for incorporating nanotubes into composite manufacturing due to their ease of handling and the ability to transfer the properties of the nanotubes into the resultant composites. Buckypapers enable thermal and electro-conductivity in ranges not possible using fiber composites alone. The objective of this research is to develop an effective, affordable manufacturing process capable of continuously fabricating buckypaper materials to meet market demands, as well as property and quality requirements from the consumers. The batch method of buckypaper manufacturing processes have been investigated and standardized by previous studies. Successful results under the standardized process have been adopted to pilot buckypaper production. Such studies have also attracted the interest of industrial consumers who require large-scale manufacturing, and continuity of buckypaper materials, which are not offered by the current batch method. Through the development of four generations of prototypes, this research has successfully designed and fabricated the Nano Material Continual Integration System (NM-CIS), a filtration system capable of producing high quality continuous buckypaper materials. A prototype to produce continuous 1.5in wide buckypapers of randomly-dispersed SWNTs has been successfully developed. Furthermore, the research has characterized the physical and electrical properties and compared them with current batch-production buckypapers. The results indicate that the continuous manufacturing processes have the potential to scale-up production of continuous buckypaper products to achieve desired quality, continuity and affordability for potential industrial applications. Furthermore, the research has designed and fabricated the MA-CIS system to fabricate continuous magnetically aligned buckypaper materials, and the W-CIS system to produce 11-in wide-buckypaper / A Thesis Submitted to the Department of Industrial Engineering in Partial Fulfillment of the Requirement for Degree of Master of Science. / Summer Semester, 2007. / June 25, 2007. / Single Wall Nanotubes, Buckypaper, Continuous Manufacturing, SWNT, Alignment / Includes bibliographical references. / Richard Liang, Professor Directing Thesis; Ben Wang, Committee Member; Chuck Zhang, Committee Member; Young-Bin Park, Committee Member; James Brooks, Committee Member.

For developing high performance carbon nanotube-reinforced polymer composites, uniform nanotube dispersion, good nanotube/matrix wetting and interfacial bonding, controlled alignment and high tube loading are critical issues. A novel technical approach using a unique buckypaper/resin infiltration method has been developed at Florida Advanced Center of Composite Technologies (FAC2T) to fabricate nanocomposites with controlled tube dispersion, orientation, and high SWNT loading. Buckypapers are thin membranes or films of preformed networks of well-dispersed SWNTs. The preformed SWNT networks are eventually transformed in the nanocomposites to construct final nanostructures in the materials. Therefore, quality buckypapers are vital for developing high performance nanocomposites. This research focuses on systematically investigating buckypaper fabrication process and characterizing the resulting buckypapers for better understanding the process and building databases of both randomly oriented and magnetically aligned buckypaper materials. The results show that the formation of buckypaper during suspension filtration can be divided into three stages: free deposition, network formation and thickness build-up. Each stage has different filtration flow rate. The results also indicated that the average thickness, weight, and area density of the aligned buckypapers are smaller than that of the random buckypapers, while the average cubic density of the aligned buckypapers is higher than that of the random buckypapers. Due to possible re-assembly of nanotubes during magnetic alignment, the average rope size of the aligned buckypapers is larger than that of the random buckypapers, and its nanostructure also has relatively larger average pore size. Furthermore, the study of cleaning residual surfactant in the produced buckypapers was also conducted. The results show 70% of the surfactant can be removed by using the proposed cleaning method. / A Thesis Submitted to the Department of Industrial Engineering in Partial Fulfillment of the Requirement for Degree of Master of Science. / Summer Semester, 2005. / June 30, 2005. / Buckypaper, Nanotube / Includes bibliographical references. / Zhiyong Liang, Professor Directing Thesis; Ben Wang, Committee Member; Okenwa Okoli, Committee Member; Chuck Zhang, Committee Member.

Non-metallic materials such as ceramics are an accepted method to produce armor systems due to their low density, high hardness, high rigidity and strength in compression. Due to ceramic's low fracture toughness and the tendency of fracturing when subject to high tensile stresses, a back-plate of a more ductile material such as aluminum, steel or fiber reinforced plastics have be used to keep the laminate intact when subjected to a projectile impact. Ceramic plates have the ability to initially slow down the bullet; then break it down into smaller fragments, but are not meant to fully stop the projectile. The ceramic plate reduces the bullets capacity to penetrate and transfer the kinetic energy from the projectile to the plate. This disperses the energy throughout a larger area thus absorbing most of the impact energy. The ceramic plate requires a backing plate for support to compensate for the brittle nature of the ceramic materials. The backing plate must be capable of containing any stray fragments and absorb some of the residual energy. The downside to this system is the total weight of the system is too large. Fiber reinforced composites have been used increasingly to replace heavier metal structures because of their high stiffness to weight ratios, corrosion resistance, damage tolerance, and functional integration. As such, new advanced fiber composites are now replacing aluminum components in the aerospace industry. Furthermore, the failure modes of composites promote pronounced energy absorption especially under high speed impact loading. This attribute has made composites valuable materials for the defeat of projectile impact and they are now increasingly being used in personnel armor like the Small Arms Protection Insert (SAPI). The current work stems form the need of the US Air Force Pararescue Jumpers (PJ). Their current SAPI equipment is a pure polymer (UHMWPE) solution that defeats the 7.62 mm rounds at muzzle velocities over 2500 ft/sec. They are however thick and heavy, making their use rather precarious in some instances. As such, a thinner, lighter and durable system is desired that retains the same properties as the current system. This work set out to investigate the viability of producing thinner and lighter cost effective plates for the defeat of the 7.62 mm rounds at muzzle velocities and criteria set by the PJSAPI specifications. The manufacturing of these plates could have a large impact on the performance of the material. Preliminary tests show that the increase in pressure applied to the laminate can increase the overall performance with a decrease in the overall weight of the system. / A Thesis Submitted to the Department of Industrial Engineering in Partial Fulfillment of the Requirements for the Degree of Masters of Science. / Fall Semester, 2007. / July 5, 2007. / SAPI, UHMWPE, Ballistics, Bullet / Includes bibliographical references. / Okenwa Okoli, Professor Directing Thesis; Ben Wang, Committee Member; Richard Liang, Committee Member.

Carbon nanotubes (CNTs) are one of the wonders of modern science. Discovered a little over 15 years ago, they have shown the research community an outstanding set of properties. In terms of mechanical properties, they exhibit extremely high young's modulus, which, coupled with a high strain to break, leads to unsurpassed strength to break. CNTs also demonstrate superior thermal conductivity, good electrical capacity and high thermal stability. In light of these properties, CNTs are expected to be introduced into a wide variety of new materials aimed at applications for various fields, such as high-performance composites, biological and chemical sensors, magnetic recording, nanoelectronic devices and flat panel displays. One such promising application is CNT-reinforced composite materials, exhibiting the possibility of outstanding mechanical properties. In practice, however, many reports indicate that nanocomposites are weaker or only slightly stronger than the neat resins. Several factors are believed to be the primary source of this discrepancy, namely poor nanotube dispersion in resin, inadequate alignment of the nanotubes, and weak interfacial bonding between nanotubes and resins. As a result, these have become crucial investigation issues for developing high-performance nanocomposites. In this dissertation, fundamental understanding of the interfacial phenomena between carbon nanotubes and polymer matrices are studied. Both molecular dynamics (MD) simulation, an effective approach to investigate nanoscale behaviors, and experimental investigation, are utilized to achieve this goal. First, we examine the interface formation phenomena between a Single Wall Carbon Nanotube (SWNT) and the resin, prior to curing, in the case of the Epon862 resin system. The MD simulation results outline the validity of some of the current theories, such as molecular migration and reduction of molecular mobility of the resin, while they seem to indicate some other mechanisms are not present in this resin system, such as molecular wrapping around the SWNTs. Second, existing MD simulation models of nanotube pullout are analyzed and modified to examine the energy of certain material systems more correctly, and to characterize interfacial shear strength in SWNT/polymer composites. The interfacial bonding and load transfer behaviors between the different SWNTs' configurations (open end, capped end, functionalized end) and three different matrices (polystyrene, polyethylene and Epon862) were examined using the modified models. The results of the modified models effectively reveal the effects of different tube configurations and resin matrices on the interfacial strength during a simulated pullout. Finally, we use MD simulation to investigate the coefficient of thermal expansion (CTE) of individual SWNTs, SWNT ropes, as well as SWNT nanocomposites. Experiments were also carried out in order to gain further insight in the results. It is found that, while the CTE of individual nanotubes is of low negative value, the CTE of the same tubes within a rope or a nanocomposite can significantly change. We also find that SWNTs can be utilized to tailor the CTE of the Epon862 resin system, depending on the functionalization of the SWNTs prior to their introduction in the resin. Finally, a new twisting vibration mode was revealed in SWNT ropes that should prove critical in further SWNT rope studies utilizing MD simulation. / 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, 2006. / November 6, 2006. / Carbon Nanotubes, Interface Formation, Thermal Expansion, Molecular Dynamics / Includes bibliographical references. / Zhiyong Liang, Professor Directing Dissertation; James Brooks, Outside Committee Member; Ben Wang, Committee Member; Chuck Zhang, Committee Member.

Polymer composite manufacturing techniques have over the years generated tremendous interest in the area of research and development in response to current trends and demands. Recent studies have focused on the development of several variations of liquid composite molding (LCM) techniques for the manufacture of polymeric composite parts. These techniques, which include processes such as Resin Transfer Molding (RTM), Vacuum Assisted Resin Transfer Molding (VARTM), Seemann Composite Resin Infusion Molding Press (SCRIMP), have gained wide spread acceptance within the composite industry, primarily because they attempt to eliminate or reduce most, of the styrene emissions associated with open mold composite manufacturing techniques. Nonetheless, LCM techniques have found limited use in the mass production sector due to long production cycle times This work is centered on the process development of the Resin Infusion between Double Flexible Tooling (RIDFT). Despite the tremendous potential benefits that can be obtained from the RIDFT process, it is still plagued by some of the inherent limitations generally prevalent amongst most closed mold technology LCM processes. These limitations arise primarily because RIDFT, just like other LCM processes, makes use of an organic peroxide based catalyst curing system that invariably introduces a certain amount of inflexibility and restriction in the overall manufacturing process. These include long production cycle times due to lengthy curing times, as well as a narrow processing window for the production of composite parts. The primary focus of this thesis is to evaluate the feasibility of designing and incorporating a Cure on Demand (C.o.D) system into the RIDFT process that would involve the use of Ultraviolet (UV) light for the curing of composite laminates. The objective is to develop a process for the RIDFT that would eliminate or reduce the inflexibility in the current production process, resulting in shortened production cycle times. UV cured laminates were produced at a fraction of the time required to produce catalyst cured laminates. Mechanical and material characterization tests were performed on each of the UV cured laminates produced. The results were referenced against that obtained for laminates produced using a catalyst curing system to determine their overall quality. The UV cured laminates after undergoing both tensile and rheological thermal tests were found to have both mechanical and material properties that were comparable and in a few instances slightly better than that of thermally cured laminates. / A Thesis Submitted to the Department of Industrial Engineering in Partial Fulfillment of the Requirements for the Degree of Master of Science. / Spring Semester, 2004. / April 15, 2004. / UV curing, Ridft / Includes bibliographical references. / Okenwa Okoli, Professor Directing Thesis; Richard Liang, Committee Member; Yaw Owusu, Committee Member.

Robust design has been gaining plenty of attention in both academia and industry over the past two and half decades. However, there is still plenty of room for improvement. In this dissertation research, several drawbacks of the existing robust design methods were identified and analyzed. These shortcomings mainly include incompatible robust parameter design and tolerance design optima, inadequate attention to internal noise factors, limitation of Steepest Descent search in parameter design process, limitation of robust design using computer experiments, limitation with the Loss Function, and insufficient connection between the academia and industry on robust design. An integrated robust design framework was proposed to help achieve robustness against both external and internal noises. A Steepest Descent Driven Parameter Design method was developed to enhance parameter design. Also developed was an improved loss function for robust tolerance design. The proposed methodology was applied using computer simulation experiments to optimize the design of a state-of-the-art injector in a High Pressure Common Rail (HPCR) injection system in a diesel engine. The injector simulation model was built using Advanced Continuous Simulation Language (ACSL) and well calibrated through extensive hardware experiments. iSIGHT, an integration and optimization software package, was utilized to assist the computer experiments. Design Experts and Minitab were used to conduct statistical designs and analysis. It was demonstrated that the injector performance was significantly improved with the proposed method. The proposed method was also compared with Taguchi's method and Response Surface Methodology based robust design method. / 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, 2006. / July 7, 2006. / Loss Function, Steepest Descent, Tolerance Design, Parameter Design, Robust Design / Includes bibliographical references. / Chuck Zhang, Professor Directing Dissertation; George Buzyna, Outside Committee Member; Ben Wang, Committee Member; Wayne A. Eckerle, Committee Member.