A coupled electromagnetic/heat transfer model capable of simulating microwave processing of composite materials in a cylindrical resonant cavity was developed. The two-dimensional model simulates processing of axisymmetric material loads in cylindrical resonant cavities operating in the TM₀₁₀ mode. The model consists of an electromagnetic model and a heat transfer model which are coupled by the heat generation term in the heat transfer equation. Heat generation in the process material is due to dielectric loss in the material and is related to the dielectric loss factor ofthe material, the processing frequency, and the magnitude of the electric field. The finite-element method was used to develop both the electromagnetic and heat transfer models. The electromagnetic model, based on Maxwell's equations, allows anisotropic conductivity and permittivity and accounts for resonance. A novel technique for determining resonance was developed for use in the electromagnetic model. The technique can be used to design microwave applicator/material systems. The heat transfer model allows anisotropic thermal conductivity and can be used to simulate heating by microwaves only, by convection only, or by a combination of microwaves and convection. The coupled model can account for the temperature dependence of dielectric properties. The electromagnetic and heat transfer models were verified by comparison to cases for which analytical solutions were available. The coupled model was then used to simulate microwave processing of nylon 66 and composite specimens of S-glass/polycarbonate. Microwave and convective heating were used alone and in combination to heat a thick cylinder of material. Comparisons are made between microwave, convective, and combined processes and the advantages and disadvantages of microwave processing are discussed. / M.S.

The common bed bug, Cimex lectularius L, has been a persistent pest of humans. Conventional pyrethroid-formulation insecticides are known to be ineffective for controlling modern bed bug populations. This study evaluates alternative treatment methods such as whole-home heat, a biological control agent (Beauveria bassiana), and the fumigant sulfuryl fluoride for control of insecticide-resistant bed bugs. Three heat systems with different energy sources (propane, electric, and glycol) were evaluated to determine attributes contributing to heat treatment efficacy. The glycol system produced the most mortality of the three systems, killing all nymphs, eggs, and most adults. Heat treatment duration and achieving lethal temperatures in complex environments were found to be the most important factors for treatment efficacy. These factors were directly correlated with technician diligence, specifically regarding monitoring surface temperatures and repositioning equipment. A formulation of B. bassiana was evaluated in the laboratory to determine its ability to infect bed bugs under varying conditions of temperature (15°C, 21°C, and 32°C) and humidity (30%, 50%, and 70%). It was found that humidity conditions (30%-50%) at ≈21°C produced the greatest bed bug mortality and the shortest bed bug median survival time. The fumigant sulfuryl fluoride was evaluated for its ability to eliminate bed bugs from motor vehicles and cargo trailers filled to 85% capacity. This study was the first to document that sulfuryl fluoride fumigation at the 1.9X dosage factor can kill all pyrethroid-resistant bed bug life stages (including eggs) in motor vehicles as well as in chambers filled with personal items. / Master of Science in Life Sciences / Since the world-wide bed bug (Cimex lectularius L.) resurgence began in the late 1990s, populations of the common bed bug have been evaluated, but most have been found to be highly resistant to pyrethroid insecticides. This resistance has been particularly troublesome due to the fact that the 1996 US Food Quality Protection Act has eliminated the use of many existing chemistries from indoor use and has inadvertently limited the development of new active ingredients for indoor use due to the cost of the required animal testing to document the No Observable Effects Level (NOEL). Due to the lack of novel chemistry for addressing modern bed bug infestations, pest management professionals have had to identify new methods for applying existing products (chemical and non-chemical) for bed bug control. This study evaluated gaseous, mechanical, and biological control methods for bed bug elimination to determine which factors contribute the most to their efficacy, as well as how these methods might be applied in novel ways for control of bed bugs in homes, personal belongings, and even vehicles. At the turn of the 20th century heat treatments were used for controlling bed bug infestations in homes and other structures. Today, mechanical heating systems are again being used to control bed bug infestations in homes and apartments. This study investigated the utility of three commercial heating systems for their ability to control existing infestations in apartment units. The three heat systems utilized different energy sources, different types of delivery equipment, and required different set up and take down procedures in apartments of different cubic footage and clutter levels. Overall, the Assault glycol heating system was found to be the most effective in its ability to get (almost) all of our hidden (in hard to heat locations) temperature sensors up to bed bug lethal temperature. Interestingly, our statistical analysis determined that getting the hard to heat locations up to lethal temperature was directly correlated with heat technician activity. The more times that the technician entered the home to monitor the treatment and adjust the equipment positions, the greater the chance of getting the hidden sensors up to bed bug lethal temperature (and killing the bed bugs). However, it was also found that none of the heat systems tested killed all of the sentinel bed bugs in every replicate. Therefore, we learned heat treatments cannot be expected to eliminate each and every bed bug in a home, and that supplemental control products such as desiccants dusts should be applied after every heat treatment. When attempting to determine which heat system was the most effective for killing bed bugs, it was determined that regardless of which heat systems was being used, the attention and activity (monitoring temperatures and adjusting equipment) of the heat treatment technician was the most important factor contributing to bed bug mortality as well as the achievement of bed bug lethal temperatures in cracks and crevices for all three systems. Our second study examined the environmental factors that influenced fungal growth after bed bug exposure to the insecticidal product Aprehend® (active ingredient Beauveria bassiana). Over the last several decades, this fungus has been widely used to control multiple insect pests. Recently, it has been labelled for bed bug control in indoor environments. This second study was intended to determine the atmospheric conditions (temperature and humidity) under which Aprehend sporulation was most effective for killing bed bugs. It was found that humidity conditions of 30-50% combined with temperatures of ~21°C produced the highest frequency of fungal infection and the shortest median bed bug survival time. This result was surprising because it was originally hypothesized that the 70% humidity condition would be equally effective for promoting fungal growth. However, at all of the temperatures tested, bed bug fungal infection rates at 70% humidity were not as high as those observed when the humidity was within the 30-50% range. Therefore, this study was able to document that the temperatures and humidity combinations that would typically be found within human homes (21oC at 30-50% humidity) were the most effective for producing fungal infections when bed bugs were exposed to the Aprehend product. The final study addressing novel methods for controlling insecticide resistant bed bugs investigated the efficacy of using Vikane gas fumigant (sulfuryl fluoride) at the 1.9× dosage rate for eliminating bed bugs in two challenging infestation situations: personal vehicles, and confined spaces densely packed with personal belongings. The vehicles used in this study were large minivans with seating that folded into the floor. The confined spaces were cargo trailers filled to 85% capacity with books, furniture, and other household items. Each van and trailer was equipped with ~90 sentinel bed bugs consisting of three groups of 9-11 bed bug eggs, 10 nymphs, and 10 adults. The Vikane Fumiguide calculator was used to determine the target dosage (g-h/m3) to apply in each replicate (e.g., one van or trailer). Sulfuryl fluoride concentrations were measured throughout the fumigation process using a Spectros SF-ReportIR. Concentration readings were input into the Fumiguide to determine when the accumulated dosage (g-h/m3) was achieved, and when aeration should be initiated. After aeration was complete, the sentinel bed bugs were removed from the replicates and bed bug nymph and adult mortality was recorded. Bed bug eggs were monitored for 23 d to determine latent mortality. Fumigated bed bug mortality for each replication was 100% regardless of life stage. Latent mortality was observed in a single bed bug egg, where the nymph never fully hatched. This study determined that fumigation with sulfuryl fluoride at the 1.9× dosage factor is an effective method for eliminating insecticide resistant bed bugs from vehicles and personal belongings in densely packed situations. Overall, it was found that the Beauveria bassiana product was most effective when applied under atmospheric conditions that are typically found in indoor home environments. This discovery was very reassuring, because the Aprehend product is one of very few that actually have residual activity with regard to bed bug control. This study also found that whole home heat treatments require rigorous pest technician attention and monitoring to achieve the best results. It was also determined that heat treatments cannot be assumed to be 100% effective on their own, and that they should be supplemented with additional (residual) treatment applications. Not surprisingly, fumigation with sulfuryl fluoride was determined to be 100% effective for eliminating bed bugs in personal belongings that had been packed into treatment chambers. The fumigation process also proved to be 100% effective for eliminating bed bug infestations in transport vehicles which cannot not be adequately treated and are at risk for having electronic components damaged if treated with heat.

The object or this experiment was to determine if and to what extent the B.O.D. of S.N.W. waste could be reduced by Heat Hydrolysis. This process gave B.O.D. reduction up to 80 percent when used on sulfite waste at Oregon State College and it was hoped that similar results could be obtained using S.N.W. liquor. The exper1mental part of the investigation was conducted to determine (1) it the B.O.D. content of S.N.W. liquor could be reduced by Heat Hydrolysis; (2) if pH, dilution and the addition of oxygen were factors that affected the reduction of B.O.D. These factors were determined by adjusting the raw liquor to the desired concentration and cooking the liquor in a closed container until certain conditions were obtained, namely, that of constant pressure with constant temperature. Ana1ysis of the raw and cooked liquor consisted of determining pH, total solids, and B.O.D., while analysis of the gas created during the cook was limited to the total amount of gas created and the amount of CO₂, CO, O₂ and H₂S in the gas. Four different series of cooks were conducted on each sample. They were, Neutral (raw liquor), Acid (raw liquor pH adjusted, Neutral-Oxygen added (raw liquor with oxygen added) and Ac1d-0xygen added (raw liquor pH adjusted with oxygen added). The samples used were 7OO ml., 465 ml., dilution 1:1 (232 ml. liquor plus 232 ml. distilled water) and dilution 2:1 (310 ml. distilled water plus 155 ml. liquor. / Master of Science

Mixture models were studied in an effort to predict the microwave frequency permittivities of unidirectional-fiber-reinforced thermoplastic-matrix composite materials as a function of fiber volume fraction, fiber orientation relative to the electric field, and temperature. The permittivities of the constituent fiber and plastic materials were measured using a resonant cavity perturbation technique at 9.4 GHz and 2.45 GHz. The permittivities of the composite specimens were measured using a reflection cavity technique at 9.4 GHz and 2.45 GHz. Simple" rule of -mixtures II models that use the fiber and plastic permittivities have been found to approximate the complex dielectric properties of the composite for varied fiber volume fractions. The permittivities of oriented composites were successfully modeled at 9.4 GHz using a tensor rotation procedure. Composite permittivities were modeled with temperature up to the glass transition temperature of the thermoplastic matrix. Good agreement was found between the mixture model and experimental results for permittivity as a function of temperature at 9.4 GHz. / Master of Science

A two-dimensional axisymmetric finite-element model developed to simulate the microwave processing of polymers and polymer-matrix composites in a cylindrical resonant cavity was improved. The model consists of two submodels: the electromagnetic submodel and the heat transfer submodel. These two models are coupled together by the heat generation term arising due to the microwave energy. A single finiteelement program was written to implement the two submodels. The heat generation term arising due to exothermic chemical reactions was added to the heat conduction equation. The model can now handle thermosetting resins as well as amorphous thermoplastic polymers. The governing equations for the electromagnetic submodel are the complex, time-harmonic Maxwell's equations. Since an axisymmetric model was developed, the material needs to be axisymmetric and centered in the cavity. The material can have anisotropic conductivity and permittivity. A separate eigenvalue code was developed to compute the resonant frequency for given cavity dimensions. This eigenvalue code can account for non-homogenous material properties. The heat transfer model is governed by the unsteady heat conduction equation with the addition of heat generation terms accounting for exothermic reactions and microwave energy. All three types of heating: microwave only, convection only, and combined microwave and convection heating can be simulated by the electromagnetic and the heat transfer models. Several test cases were run to validate the programs. The results of the eigenvalue code were compared to those published in the literature. Simple test cases for which analytical expressions are available were run to verify the electromagnetic and heat transfer submodels. Excellent agreement was obtained in all of the comparisons. Once the programs were validated, several simulations were done to study microwave processing and/or convective heating of polymers and polymer-matrix composites. The materials considered were nylon 66, S-glass/polycarbonate composite, and S2-glass/epoxy composite. To study the advantages and disadvantages of microwave processing over conventional processing, comparisons were'made between the simulations of the two processes. / Master of Science

A computer model for diffusion-controlled internal precipitation was used to simulate the corrosion behavior of Ni-based superalloys in carburizing atmospheres. The model is based on Crank-Nicholson finite difference solution of the diffusion equation. The code also includes the ternary cross diffusion effect due to substitutional alloying elements that are preferentially oxidized. The model can treat two sets of boundary conditions corresponding to the presence or absence of a protective oxide scale. It accounts for internal precipitation of corrosion products whenever thermodynamic solubility limits are exceeded. Up to four different carbides can be treated simultaneously. The solubility product is computed for each reaction and the amount of carbon that reacts is removed from the diffusion process. Under non-protective conditions, the predictions of model were compared to carburization profiles obtained experimentally in H₂-CH₄ environment tests. Results are presented for the formation of Cr, Mo, Ti, W, and Nb carbides in Ni-based superalloys. The predicted corrosion profiles are in qualitative agreement with experimental data. / Master of Science

The purpose of this work was to develop a steel tempering model that is useful to the commercial heat treater. Most of the tempering models reported address isothermal conditions which are not typical of most heating methods used to perform the tempering heat treatment. In this work, a non-isothermal tempering model was developed based on the tempering response of four steel alloys. This tempering model employs the quantity resulting from the numerical integration of the time-temperature profiles of both the heating and cooling portions of the tempering cycle. The model provided a very good agreement between experimental and predicted hardness when secondary hardening did not occur. The developed tempering model was then used as the basis for a process simulation model of a large indirect gas-fired furnace. Unlike the small-scale laboratory experiments performed in the development stage of this work, the temperature variation in this furnace was significant. Recording the temperature with time at 29 locations within the furnace allowed for suitable characterization of the temperature variation. The thermal data was used as inputs in a finite element method model and the time – temperature profiles of three production heavy truck side rails were then simulated. The tempering model provided a good prediction of the tempered hardness compared to experimental measurements. Finally, conclusions are drawn and suggestions are made for future work. / Ph. D.

Thesis (M. Tech. (Engineering: Mechanical)) -- Central University of Technology, Free State, / The Centre for Rapid Prototyping and Manufacturing (CRPM) at the Central University of Technology, Free State (CUT) manufactures implants using Electro Optical Systems (EOS) titanium Ti-6Al-4V alloy powder (further referred to as EOS Ti64 powder) by means of Direct Metal Laser Sintering (DMLS) process on the EOSINT M 270 machine. For this reason, there is a need to characterise and acquire knowledge of the basic properties of direct metal laser sintered EOS titanium Ti-6Al-4V alloy samples (further referred to as DMLS Ti64 samples) under static tensile loading in order to provide the CRPM with engineering design data. The first objective of this Master’s study is to acquire the characteristics of EOS Ti64 powder in order to ascertain its suitability in the DMLS process. Secondly, the study aims to assess tensile properties and elastic constants of DMLS Ti64 samples produced from the set process parameters of EOSINT M 270 machine. Thirdly, it is to investigate microstructures of DMLS Ti64 samples subjected to different heat treatment techniques which will eventually assist in the determination of a suitable heat treatment technique that will yield higher ductility. Finally, the study aims to validate the static behaviour of DMLS Ti64 samples subjected to the static tensile loading up to a yield point in order to determine failure due to yielding. The samples were manufactured at CRPM Bloemfontein. The metallographic examinations, heat treatment and the determination of mechanical properties were done at the CSIR in Pretoria. Optical Microscope (OM) and Scanning Electron Microscope (SEM) were used to determine microstructures of DMLS Ti64 samples while Energy Dispersive X-Ray (EDX) analyses were performed using SEM. The samples were heat treated at temperatures of 700, 1000 and 1100°C respectively, and subsequently either cooled with the furnace, air or were water quenched. The mechanical property tests included tensile, hardness and determination of elastic constants. The static behaviour of DMLS Ti64 samples under static tensile load up to a yield point was predicted and verified using ABAQUSTM Finite Element Analysis (FEA). The stress-strain curves from ABAQUSTM were interpreted using MDSolid program. The point of interest was Von Mises yield stress at 0.2% offset, in order to determine failure due to yielding. EOS Ti64 powder particles were spherical in shape and the alpha and alpha+beta phases were identified. As-laser sintered samples possess a very fine and uniform alpha case with islands of martensitic plates; samples were brittle and showed low levels of ductility with an average elongation of 2.6% and an area reduction of 3.51%. Ultrasonic test results showed that DMLS Ti64 samples have Young’s modulus of 115 GPa, Shear modulus of 43 GP, a bulk modulus of 109 GPa and Poisson’s ratio of 0,323 while the density was 4.4 g/cm3. Slow cooling of DMLS Ti64 samples from 1000 and 1100oC resulted in a microstructure constituted more by the alpha phase of lower hardness than those from 700oC and as-laser sintered samples. High hardness was obtained by water quenching. The water quenched samples showed martensitic transformation and high hardness when compared to furnace cooled samples. Beta annealing tailored a microstructure of as-laser sintered samples into a lamellar structure with different lath sizes as per cooling rate. Beta annealing improved ductility levels up to 12.67% elongation for samples furnace cooled for 4 hours and even higher to 18.11% for samples furnace cooled for 34 hours, while area reduction increased to 25.94% and 33.39%, respectively. Beta annealing conversely reduced yield strength by 19.89% and ultimate tensile strength was reduced by 23.66%. The calculated maximum Von Mises stresses found were similar to the FEA interpreted results. The average percentage error, without the stress concentration factor, was approximately 8.29%; with the stress concentration factor included, it was 0.07%. The small reaction forces induced in both x-axis and z-axis contributed to this error of 0.07% between the calculations and ABAQUSTM FEA results. Samples that were not heat treated fell outside the Von Mises criterion and failed due to yielding. This justified the brittleness found in the tensile test results where elongation and area reduction were 2.6% and 3.51% respectively. However, all samples that were heat treated fell within the Von Mises criterion. The objectives of this study were achieved; the mechanical properties were similar to those of standard specification for wrought annealed Ti-6Al-4V alloy for surgical implant applications and EOS GmbH manufacturer’s material data sheet. DMLS Ti64 samples must be beta annealed in order to attain higher levels of ductility. A recommendation was made to further investigate the effect of heat treatment on the other mechanical properties. Furthermore, detailed results of basic properties of DMLS Ti64 samples are provided in the appendices in chart format and were written on a CD disc.

The need for clean and renewable fuel such as hydrogen is driven by a growing worldwide population and increasing air pollution from fossil fuels. One of the major barriers for the use of hydrogen in automotive industry is the storage of hydrogen. Physisorption is the most promising storage technique due to its high storage density, reversibility and rapid sorption kinetics besides being safe and volume-efficient. A major challenge for physisorption is the need to manage the heat of adsorption at cryogenic temperatures. In this thesis, a 6061 aluminum microchannel cooling plate is designed to remove the equivalent heat flux required by the adsorption of hydrogen within an adsorption bed. Therefore, the objective of this thesis is to determine whether laser welding and heat treating strategies can be developed for a 6061 aluminum microchannel cooling plate as part of a larger hydrogen storage thermal management system. Key manufacturing process requirements include controlling the hermeticity, strength and dimensional stability of the heat-treated weld joint. A hermetic microchannel cooling plate was successfully laser welded and heat treated using free convection in air to quench the solution heat treatment. The weld strength and warpage obtained were within acceptable limits. Experimental testing of the fabricated microchannel cooling plate showed acceptable percent error with an experimental heat removal rate within 13.4% of computational fluid dynamics (CFD) analyses and an average pressure drop error of 25%. Calculations show that the cooling plate developed could support a hydrogen storage thermal management system taking up 5.0% and 10.3% of the system displacement volume and mass, respectively. / Graduation date: 2013

Over the last few decades, body-centered-cubic (bcc) beta (β) titanium alloys have largely been exploited as structural alloys owing to the richness in their microstructural features. These features, which lead to a unique combination of high specific strength and ductility, excellent hardenability, good fatigue performance, and corrosion resistance, make these alloys viable candidates for many applications, including aerospace, automobile, and orthopedic implants. The mechanical properties of these alloys strongly depend on the various phases present; which can be controlled by thermomechanical treatments and/or alloy design. The two most important and studied phases are the metastable ω phase and the stable α phase. The present study focuses on the microstructural evolution and the mechanical behavior of these two phases in a model β-Ti alloy, binary Ti-12wt. %Mo alloy, and a commercial β-Ti alloy, β-21S. Microstructures containing athermal and isothermal ω phases in the binary Ti-12wt. %Mo alloy are obtained under specific accurate temperature controlled heat treatments. The formation and the evolution of the ω-phase based microstructures are investigated in detail via various characterization techniques such as SEM, TEM, and 3D atom probe tomography. The mechanical behavior was investigated via quasi-static tensile loading; at room and elevated temperatures. The effect of β phase stability on the deformation behavior is then discussed. Similar to the Ti-12wt. %Mo, the formation and the evolution of the athermal and isothermal ω phases in the commercial β-21S alloy was studied under controlled heat treatments. The structural and compositional changes were tracked using SEM, TEM, HR-STEM, and 3D atom probe tomography (3D-APT). The presence of additional elements in the commercial alloy were noted to make a considerable difference in the evolution and morphology of the ω phase and also the mechanical behavior of the alloys. The Portevin-Le Chatelier (PLC) like effect was observed in iii this alloy at elevated temperature and this has been attributed to the shearing of the ω precipitates and the dynamic precipitation of the α phase within these channels. The formation of the stable α phase in the commercial β-21S alloy due to the influence of precursor phases, like the metastable ω phase, is investigated. It is evident from the microstructural characterization, using SEM, TEM, HR-STEM, and 3D-APT, that the ω phase does play a role on the fine scale α precipitation. The mechanical behavior of the β+α microstructure, investigated via tensile testing, shows that these alloys are ideal candidate for precipitation hardening. The exceptional strength values obtained in this alloy have been attributed to a combination of several factors.