Since the discovery of carbon nanotubes in 1991 alongside their superior performance in mechanical and electrical properties, carbon nanotubes have been widely considered to be one of the most promising next generation materials. They have been frequently used in polymer composites due to their high strength-to-weight and modulus-to-weight ratios. Yet despite their promising qualities in manufacturing, carbon nanotube based composites still have many issues that need to be resolved before they can be used for industrial applications. In order to more cost effectively produce nanocomposites and improve their quality, it is necessary to accurately observe and understand the variations in their raw material properties. The variability of the raw material in nanotube based composites usually has a large impact on the properties of the eventual product. However, physical experimentation for the purpose of quantifying variability in nanomaterial properties is usually expensive and sometimes not feasible or accurate enough. This paper presents a constrained nonlinear programming approach for the quantification of raw material variability while also examining the impact of raw material variability on the properties of buckypaper polymer (BPP) composites. The proposed approach suggests conducting small physical experiments to collect data on raw material properties and final composite part properties before employing an inverse uncertainty propagation approach to estimate the parameters of the probability distribution of the material properties. Both univariate and multivariate probability distributions are considered. A case study based on data from a real buckypaper manufacturing process is used to illustrate the approach. It is shown that simultaneously modeling the material properties with a multivariate distribution improves the quality of the identified model. / 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, 2010. / June 11, 2010. / Uncertainty Quantification, Monte Carlo Simulation, Nonlinear Programming, Nanocomposites / Includes bibliographical references. / Arda Vanli, Professor Directing Thesis; Joseph Pignatiello, Committee Member; Chad Zeng, Committee Member; Ben Wang, Committee Member; Chuck Zhang, Committee Member.

Since their discovery in 1991, carbon nanotubes have undergone intensive research. The single-walled carbon nanotube, or SWNT, has a unique electronic structure. According to their chirality, they can be either metallic or semiconductors with various band gaps. These different electronic structures influence their electrical and thermal properties. Studies have been conducted to understand, model and measure their electrical and thermal properties by computer simulation and experimental measurements. Even though current research shows inconsistent results, all studies show that SWNTs have phenomenal electrical and thermal properties. To take advantage of these unique properties of nanotubes requires properly incorporating SWNTs into a matrix as a reinforcement or filler to form nanocomposites with desired properties. Carbon nanotube reinforced composites are still under development. The mechanical properties of these materials have been intensively explored; however, the electrical and thermal properties still require further study. The main objective of this thesis was to measure and understand the thermal behavior of SWNT-reinforced composites. This thesis focuses on 1) the thermal conductivity of buckypapers (aligned or random SWNT network from filtration of well-dispersed nanotube suspension) and the nanocomposites produced from the buckypapers, and 2) the influence of nanotubes on thermal expansion by direct mixing and casting samples of SWNT/epoxy nanocomposites. Thermal conductivity was measured using a comparative method, with a constantan foil as a reference. The temperature dependence of the thermal conductivity was measured from 115 K to room temperature. Magnetically aligned buckypapers produced with 17.3 Tesla magnetic field showed the highest thermal conductivity at room temperature, with a maximum value of 41.5 W/mK in the aligned direction. The coefficient of thermal expansion (CTE) was measured using the Thermomechanical Analyzer (TMA). The influence of nanotube functionalization and loading on the CTE of the epoxies revealed that adding 1 wt% nanotubes in the epoxy resin could reduce the CTE of the resin as much as 35.5%. The mechanisms of thermal conductivity variation and CTE reduction in the buckypapers and nanocomposites are also discussed. / A Thesis submitted to the Department of Industrial Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester, 2004. / July 12, 2004. / Carbon Nanotube, Buckypaper, Thermal Conductivity, CTE / Includes bibliographical references. / Zhiyong Liang, Professor Directing Thesis; James Brooks, Committee Member; Ben Wang, Committee Member; Chuck Zhang, Committee Member.

Carbon nanotubes (CNTs) have drawn interest for many applications since their discovery. While they provide exceptional mechanical, physical and chemical properties, several technical barriers must be overcome before these properties can be fully used. Some of such drawbacks concern length control, lack of good dispersion and poor interfacial bonding. Currently, CNTs such as single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) and carbon nanofibers (CNFs) are produced in lengths ranging between several to hundreds micrometers and are usually bounded into macroscopically entangled networks. This contradicts with the requirements of some applications, which in the end will benefit with short and highly dispersed CNTs in lengths of a few hundred nanometers or less, such as drug delivering and energy storage carriers. Short CNTs (s-CNTs) and CNFs (s-CNFs) can enhance the mechanical properties of a composite due to the increased interaction with the polymer matrix, through the improvement of the interfacial bonding and resin encapsulation, which is possible with existing open ends of nanotubes. Ultimately this influences the matrix's properties by affecting its chain entanglements, morphology, and crystallinity in the nanocomposite. This research is a continuous effort on nanoscale cutting and characterization of s-CNTs and s-CNFs. Moreover, this research used s-MWNTs and s-CNFs in the lengths of 200 and 500 nm to manufacture the nanocomposites. The mechanical properties of the resultant nanocomposties were characterized. The interactions of the s-MWNT and s-CNTs with epoxy resin matrix were observed using high-resolution SEM and atomic-resolution TEM. The results were compared to nanocomposites with pristine MWNTs and CNFs. In the study, four case studies were explored: 1) 200 nm s-MWNT/epoxy composites; 2) 500 nm s-MWNTs/epoxy composites; 3) 200 nm s-CNF/epoxy composites; 4) 500 nm s-CNF/epoxy composites. For all four cases the MWNT and CNF concentrations were 0.05 wt%, 0.10 wt%, and 1.00 wt%, respectively. Significant mechanical improvements were observed. The strength of the s-MWNT nanocomposite at 1.00 wt% gave a 64% improvement compared to the control sample. The highest young's modulus was also obtained in the 1.00 wt% s-MWNT (200 nm) nanocomposite, and it showed an increase of 44%. In general, the most significant improvements were seen with the s-MWNTs (200 nm) nanocomposites due to their smaller diameters and shorter length. Glass transition temperature was also studied. Finally, the interfacial bonding and interactions of the nanotube's opened ends with the resin matrix were observed through HR-SEM and atomic-resolution TEM analysis, which validated the creation of MWNT and CNF opened ends and the actual resin encapsulation inside the nanotubes' hollow structures. / 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, 2011. / April 27, 2011. / short carbon nanotubes, open ends nanocomposites / Includes bibliographical references. / Zhiyong Richard Liang, Professor Directing Thesis; Tao Liu, Committee Member; Chun Chuck Zhang, Committee Member.

The current research studied the idea of introducing energy-absorbing polymers – specifically high-density viscoelastic polyurethanes – to reduce the blunt trauma from residual impact energy. This work investigated the material properties of viscoelastic polyurethane foams and the efficacy of the addition of an energy absorbing material to protective garments for reducing blunt trauma under low-velocity impact. The research also provided a methodology for testing composite plates backed by soft materials during low-velocity impact tests. The thickness of the backing material was proven the most influential factor in energy absorption during impact. Finally, using optimization tools, a suggested thickness and bonding condition was given for the implementation of viscoelastic foam in protective garments. / A Thesis Submitted to the Department of Industrial Engineering in Partial Fulfillment of the Requirements for the Degree of Master of Science. / Spring Semester, 2008. / November 21, 2007. / Polyurethane Foam, Impact, Blunt Trauma, Composite / Includes bibliographical references. / Okenwa O. I. Okoli, Professor Directing Thesis; Samuel Awoniyi, Committee Member; James Simpson, Committee Member; Ben Wang, Committee Member.

This research presents a study on an innovative composite manufacturing process called Resin Infusion between Double Flexible Tooling (RIDFT). In this process, resin is infused between two flexible tools through fiber reinforcements in a two-dimensional flat shape. The wetted reinforcements and flexible tooling are then formed over a mold into a specified part shape by use of vacuum. The RIDFT process has potentials for rapidly and affordably producing large composite parts. This research details the development of the industrial RIDFT machine from its design to its fabrication and to the demonstration of its use. This new machine uses new techniques, integrating vacuum sealing, dynamic supporting and temporary resin distribution channels to achieve industrial application requirements. A design of experiment (DOE) approach is used to perform testing and analysis to validate the ability of the RIDFT process to form various geometries and identify limitations in formability and issues with wrinkling. Four specific fiber textile structures were studied in their ability to form over a half sphere of varying radii and a rectangular mold of varying corner radii. The number of fiber layers was also studied to understand the effects on forming. Fiber textile structure and fiber layers were shown to be significant for their influence on formability and wrinkling. To better understand the forming mechanics within the RIDFT process and to predict the formability of a desired geometry, a simulation model was required. The PAMFORM software was chosen for modeling because it is a general-purpose finite element package for the industrial virtual manufacturing of non-metallic sheet forming. PAMFORM is unique in its ability to model a variety of forming processes. This research details the development of the simulation model for the RIDFT process based on PAMFORM and describes the validation of the model through experimental methods. This development includes the modeling of multiple layers of resin-wetted reinforcements, silicone diaphragms and part geometries, as well as the modeling of contact interfaces and forming pressures. The systematic investigation has been done for characterizing fabric drapability, rubber deformation and friction interactions for developing the simulation model. The model results are then compared against experimental results for model validation. This validated model will allow the ability to predict drapability and fiber deformation during the process forming. The results of the simulation reveal mechanisms and influence factors of the drapability and wrinkling of the RIDFT process. / A Dissertation Submitted to the Department of Industrial Engineering & Manufacturing Engineering in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy. / Fall Semester, 2003. / November 10, 2003. / RIDFT, Resin Infusion, Drapability, Manufacturing, Composites, Simulation / Includes bibliographical references. / Zhiyong Liang, Professor Directing Dissertation; Ching-Jen Chen, Outside Committee Member; Ben Wang, Committee Member; Chuck Zhang, Committee Member; James Simpson, Committee Member.

General augmentation techniques such as foldover and semifold have been a common practice in industrial experimentation for many years. Even though these techniques are extremely effective in maintaining balance and orthogonality, they possess serious disadvantages such as the inability to decouple specific terms and a high level of inefficiency. This dissertation aims for a sequential experimentation approach capable of improving the drawbacks of the general methods while maintaining some of its benefits. Chapter 3 begins with proposing an algorithm for sequential augmentation of fractional factorial designs resolution III. The proposed algorithm is compared with its competitors, semifold and foldover using simulated data under 3 noise level conditions. Advantages, limitations, and potential benefits of the new method are provided. Chapter 4 explores new possibilities for augmentation of efficient mixed-level designs (EAs). Current augmentation methods for mixed-level designs include only the optimal foldover plans developed by Guo (2006). Semifold plans for several mixed-level designs are developed by selecting half of the treatment combinations of the foldover fraction using the general balance metric criterion and an exhaustive search approach. Chapter 5 complements this research by providing a methodology for sequential augmentation of mixed resolution robust designs. The work presented here extends the current limits of sequential experimentation for resolution III, mixed-level and robust designs and provides a viable alternative for the experimenter in situations in which financial restrictions do not allow the implementation of a general 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, 2008. / July 11, 2008. / Semifold, Foldover, Level, Mixed, Robust, Resolution, Sequential, Experimental Design / Includes bibliographical references. / James R. Simpson, Professor Directing Dissertation; Fred Huffer, Outside Committee Member; Joseph J. Pignatiello, Jr., Committee Member; Marcus Perry, Committee Member.

Electrically conductive polymers (ECPs), offering capabilities such as electrostatic discharge protection and electromagnetic interference shielding, have been the subject of intensive research and development both in academia and industry. The emergence of new conductive nano-fillers in recent decades, particularly carbon nanotubes (CNTs), further fuels more enthusiasm. Thanks to CNTs' excellent mechanical, thermal, and electrical/electronic properties, CNT-filled polymers possess not only conductive properties, but a range of other properties desirable for multi-functional and high performance applications. In order to fully exploit the benefits of CNT-based conductive polymers (CNT-ECPs), researchers have conducted diverse studies primarily to characterize the electrical conductivity of the composites. A crucial area that is less studied is the piezoresitive behaviors of CNT-ECPs, that is, the change in material conductive properties due to an applied stress or strain. Given broad usage of ECPs, it would be reasonable to assume that ECP products commonly operate under certain stress or strain conditions. For instance, an electrostatic discharge (ESD)-protected conductive coating for spacecraft would be affected by strain induced by mechanical or aerodynamic loads. A more systematic understanding of the materials' piezoresistivity, therefore, is instrumental in ensuring satisfactory conductive performance of those material applications. Additionally, knowledge of conductive characteristics of the CNT-ECPs against stress/strain can open the door to newer material applications, e.g., strain gage or multifunctional conductive coating with strain-sensing capability. This research aims to achieve a more fundamental understanding of the mechanism of piezoresistive property of CNT-ECPs, and to develop a model that permits quantifying the structure-property relationships of CNT-ECPs' piezoresistivity. In this research, expanded experimental studies with various thermoplastic CNT-ECPs revealed that piezoresistivity in CNT-ECPs is dominated by changes in inter-tube resistances. Additionally, the gauge (sensitivity) factors of the CNT-ECPs follow an exponential relationship with (v – vc), where v is the volume concentration of CNT in the composite and vc is the tube volume concentration at its percolation threshold. The model development effort yielded a semianalytical piezoresistivity model capable of analyzing and predicting piezoresistivity in three-dimensional CNT-ECP samples. The model is most applicable to systems with straight short MWNTs randomly dispersed in thermoplastic polymers. / A Dissertation Submitted to the Industrial & Manufacturing Engineering Department in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy. / Fall Semester, 2008. / November 07, 2008. / Nanocomposite, Sensor, Percolation Theory / Includes bibliographical references. / Zhiyong (Richard) Liang, Professor Directing Dissertation; Chuck Zhang, Committee Member; Joseph J. Pignatiello, Jr., Committee Member; Young-Bin Park, Committee Member; Petru Andrei, Outside Committee Member.

Most of the Federal Motor Vehicle Safety Standards applicable to school buses do not specifically cover the cutaway type of buses assembled on ladder-type chassis, for which a production process is split into two stages. In the first stage, the chassis and cab section are assembled by automobile manufacturers. In the second stage, the vehicle is shipped to another company where the bus body and additional equipment are installed. Lack of strict structural standards for transit bus body builders necessitates the crashworthiness and safety evaluation of this category of vehicles. Such an assessment process is imperative since these transit buses are often used to transport disabled passengers. A full scale crash test is considered the most reliable source of information regarding structural integrity and safety of motor vehicles. However, the high cost of such tests and difficulties in collecting data results in an increasing interest in the analytical and computational methods of evaluation. Theses methods allow for extensive safety studies once the finite element model is validated. A reliable analytical investigation can reduce the cost dramatically and allow faster introduction of the new solutions. This thesis research work presents the procedure for development of a finite element (FE) model of a public transit bus and the results of its crashworthiness and structural integrity analysis. The finite element model was developed based on the geometry obtained by disassembling and digitizing all major parts of the actual bus. The FE model consists of 73,600 finite elements, has 174 defined property sets (groups of elements with the same features) and 23 material models. All parts are connected using different multi point constraints and special links with failure to model actual types of structural connections such as bolts and spot welds. LS-DYNA non-linear, explicit, 3-D, dynamic FE computer code was used to simulate behavior of the transit bus under different impact scenarios, such as frontal impact and side impact at various velocities. / 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, 2003. / November 10, 2003. / Analysis, Element, Finite, FEM, FEA / Includes bibliographical references. / Okenwa Okoli, Professor Directing Thesis; Jerry Wekezer, Committee Member; Robert Braswell, Committee Member.

Poisson count process are often used to model the number of occurrences over some interval unit. In an industrial quality control setting, these processes are often used to model the number of nonconformities per unit of product. Current methods used for monitoring and estimating changes in Poisson count processes assume that the magnitude and type of change are known a priori. Since rarely in practice are these known, this dissertation reports on the development and evaluation of several methods for detecting and estimating change points when the magnitude and type of change are unknown. Instead, the only assumption requires that the type of change belongs to a family of monotonic change types. Results indicate that the methodologies proposed throughout this dissertation research provide robust detection and estimation capabilities (relative to current methods) with regard to the magnitude and type of monotonic change that may be present. / A Dissertation Submitted to the Department of Industrial Engineering in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy. / Summer Semester, 2004. / May 28, 2004. / Maximum Likelihood Estimation, Hypothesis Testing, Quality Control, Special Cause Identification, Statistical Process Control, Poisson Count Processes, Process Improvement, Change Point Estimation, Likelihood Ratio, Change Point Detection, Average Run Length, Order-Restricted Inference, CUSUM Control Chart, PAV Algorithm / Includes bibliographical references. / Joseph J. Pignatiello, Jr., Professor Directing Dissertation; Anuj Srivastava, Outside Committee Member; James R. Simpson, Committee Member; Chuck Zhang, Committee Member.

Proper function of traffic photometric devices such as traffic signal modules is crucial for safe operation in the traffic environment. The Traffic Engineering Research Lab (TERL) of Florida Department of Transportation (FDOT) has a significant role in ensuring that these devices perform in accordance to specified standards at all times. Therefore it is necessary that this lab is equipped with the right kind of test facility and procedures, thus enabling device performance verification be done periodically in addition to new device qualifications. The Institute of Transportation Engineers (ITE) specification is used as one of the governing documents. This research will describe an investigation performed upon the test procedure for light emitting diode (LED) signal modules. The purpose of the investigation was to identify variability in procedure activities and to determine the overall test procedure primarily using design of experiments methodology and other statistical analysis approaches. Data analysis by this methodology was essential to characterize process variability because the test procedure execution requires management of six input factors which were not previously tested for significance. Findings from this work are also used to recommend to the lab management on issues about potential facility upgrades. Recommendations were also provided to the ITE to explore the validity of their data from statistical perspective. This research improved the test procedure for testing LED signal modules which will permit further determination of other photometric devices test procedures. / A Thesis Submitted to the Department of Industrial Engineering in Partial Fulfillment of the Requirements for the Degree of Masters of Science. / Summer Semester, 2006. / July 10, 2006. / Test Procedure, Design of Experiments, LED Signal Module, Spectrascan Colorimeter / Includes bibliographical references. / James R. Simpson, Professor Directing Thesis; Joseph J. Pignatiello, Jr., Committee Member; Okenwa Okoli, Committee Member.