Theoretical models are developed to predict the nature of the elevated temperature failure behavior in composites containing bridged cracks under small-scale creep conditions both for intermittently (or quasi-statically) and continuously growing matrix cracks that are fully bridged by continuous ceramic fibers. The time-dependence (or rate-dependence) in these models arises as a result of the presence of a viscous fiber/matrix interfacial layer. Under load this layer undergoes shear flow causing time-dependent pull-out of bridging fibers from the crack surfaces. The mechanics of time-dependent bridging is combined with a failure criterion based on secondary failure in a crack-tip creep process zone. The dependence of the matrix creep crack growth rates on flaw size and crack wake parameters as well as on composite microstructure is derived. It is shown that the crack wake plays a predominant role in influencing not only the magnitude of creep crack growth rates but also the relationship of growth rates to the crack sixes. The implications of the results for elevated temperature composite component design are discussed.

Plans for development of human colonies on the Moon, Mars or other planets will require the investigation of new structural materials. In order to foster self-sufficiency and to make the colonies economically feasible, materials must be developed from locally available resources when possible. In this investigation a material made from a lunar soil simulant has been developed and tested for its mechanical properties. The simulant was mixed with varying percentages of aluminum, stainless steel and carbon steel fibers and heated to 1100°C to form a solid material. Beam shaped samples were cut from these specimens for bending tests. From the intact portions of the tested beams, samples for compression testing were cut and tested. Analysis of the results includes bending strength, compressive strength, and investigation of elastic moduli. The material was found to have significant strength in bending and compression. Results indicate the presence of fibers significantly changes the behavior of the material.

An analytical model for the specific gas detection of oxygen, carbon dioxide, and water vapor using zirconia amperometric oxygen sensors has been developed. Sensors of this type have been designed, fabricated, and tested using planar ceramic technology. Furthermore, an experimental setup has been designed and constructed for sensor characterization. This testbed can accurately control gas partial pressures as well as the total system pressure over a wide range of flow rates. Extensive effort has been put into design and construction of this testbed to ensure accurate scientific measurements. Special attention has been paid to ensuring that the apparatus is leak-tight from air to ensure accurate measurements at low oxygen partial pressures. Results of the experimentation for oxygen detection as well as the detection of carbon dioxide and water vapor are presented. The effects of electronic conduction in the zirconia electrolyte at low oxygen partial pressures are examined. Possible applications of the sensor, as well as suggestions for further research are discussed.

<p> This study develops a novel sandwich composite material using plant based materials for potential use in nonstructural building applications. The face sheets comprise woven hemp fabric and a sap based epoxy, while the core comprises castor oil based foam with waste rice hulls as reinforcement. Mechanical properties of the individual materials are tested in uniaxial compression and tension for the foam and hemp, respectively. The sandwich composite is tested in 3 point bending. Flexural results are compared to a finite element model developed in the commercial software Abaqus, and the validated model is then used to investigate alternate sandwich geometries. Sandwich model responses are compared to existing standards for nonstructural building panels, showing that the novel material is roughly half the strength of equally thick drywall. When space limitations are not an issue, a double thickness sandwich biocomposite is found to be a structurally acceptable replacement for standard gypsum drywall.</p>

<p> Different positions of a material used for structures experience different stresses, sometimes at both extremes, when undergoing processing, manufacturing, and serving. Taking the three-point bending as an example, the plate experiences higher stress in the middle span area and lower stress in both sides of the plate. In order to ensure the performance and reduce the cost of the composite, placement of different composite material with different mechanical properties, i.e. selective reinforcement, is proposed. </p><p> Very few study has been conducted on selective reinforcement. Therefore, basic understanding on the relationship between the selective reinforcing variables and the overall properties of composite material is still unclear and there is still no clear methodology to design composite materials under different types of loads. </p><p> This study started from the analysis of composite laminate under three point bending test. From the mechanical analysis and simulation result of homogeneously reinforced composite materials, it is found that the stress is not evenly distributed on the plate based on through-thickness direction and longitudinal direction. Based on these results, a map for the stress distribution under three point bending was developed. Next, the composite plate was selectively designed using two types of configurations. Mathematical and finite element analysis (FEA) models were built based on these designs. Experimental data from tests of hybrid composite materials was used to verify the mathematical and FEA models. Analysis of the mathematical model indicates that the increase in stiffness of the material at the top and bottom surfaces and middle-span area is the most effective way to improve the flexural modulus in three point bending test. At the end of this study, a complete methodology to perform the selective design was developed.</p>

Thallium based superconductors have the highest, reproducible transition temperatures to date, $\rm Tl\sb2Ba\sb2Ca\sb2Cu\sb3O\sb{x},$ at 122 K. Difficulty arises in preparing these materials using the common "shake and bake" procedure. The high temperature stability of BaCO$\sb3$ and the volatility of the $\rm Tl\sb2O\sb3$ pose additional problems which appear to be insurmountable. Thus, it is necessary to investigate alternative routes. / The use of a single phase precursor is an attractive option. One could pre-react the Ba-Ca-Cu starting materials and, in the final step, add an appropriate amount of $\rm Tl\sb2O\sb3$. The mixture would then be fired for a short period of time, preferably at temperatures below the volatility of $\rm Tl\sb2O\sb3$. / In order to successfully use a precursor route, the chemistry of the precursor material must be understood. The ternary BaO-CaO-CuO system is not well characterized. A methodical investigation of this system will provide a better understanding of the chemistry involved. / Presented in this paper is an investigation of selected regions of the ternary phase system. Two alternative preparative methods will be compared the common "shake and bake" method. Effects of time and heating temperature of these materials are examined and presented. / Source: Dissertation Abstracts International, Volume: 55-04, Section: B, page: 1412. / Director: Ronald J. Clark. / Thesis (Ph.D.)--The Florida State University, 1994.

Nanomaterials have unique physics and chemistry properties compared with their bulk counterparts and have been widely studied in different fields ranging from energy to biomedicines. This thesis investigates controlled synthesis of gold nanomaterials, the heating and interactions of gold nanomaterials with external electromagnetic and ultrasonic fields, and their potential applications in non-invasive heat-related biomedicines. Gold nanomaterials have been synthesised by the citrate reduction method with the aid of ultrasonification. Through ultrasonification, the size of obtained spherical GNPs can be controlled between 10nm and 15nm, and the prepared nanoplates can be controlled between 50 nm to 150 nm. Purification process has been performed through membrane dialysis, in order to obtain pure nanoparticles for investigating the heating behavior of nanoparticle dispersions under EM/ultrasound field and elucidating the impurity effect. Moreover, the purified gold nanoparticles have been characterized by various means, such as FTIR, atomic absorption spectrometer, zetasizer, SEM, TEM and UV-Vis absorption for the purpose of fully understand the properties of gold nanoparticle in terms of purity, concentration, size, morphology and optical properties. The bulk heating effects of low-concentration GNPs have been investigated by using ultrasonic field, electromagnetic (EM) field, and laser irradiation. The results have shown that significant bulk temperature increase can be achieved for the lowconcentration gold nanoparticle dispersions under ultrasonic field, the EM field at 200 kHz and 400 kHz, and laser irradiation. Comparatively, the purified GNPs did not show significant heating effect under the EM fields of 13.56 MHz and 2.45 GHz. 6 Different mechanisms are thereby discussed to explain the heating effects. While some can be explained by established theories, such as the ultrasonic and laser heating, it is still unclear about the heating effect under low frequency EM field. A few possible reasons could be attributed to the changes of the dielectric properties and the electrophoresis effect. In addition, GNP incorporated microcapsules have been fabricated through the layer-bylayer technology, and laser treatments of the microcapsules embedded with different shapes of gold particles have been studied. The results have shown that matching between the laser wavelength and the absorption band of gold nanoparticles, which can be shifted by controlling the morphology of nanoparticles, is a prerequisite to achieve the maximum heating effect to deform the microcapsules and hence to present the microcapsules for biomedical uses. In vitro (B50 cell) and in vivo (fruit fly) studies of the biocompatibilities of our synthesised GNPs have been exanimated. The results demonstrated that the GNPs have high biocompatibility for B50 cells and fruit flies. GNPs assisted laser treatment of B50 cells has shown faster thermal damage to the cells in contrast to the cells without addition of GNPs. Keywords: nanomaterial, gold nanoparticle, capsules, hyperthermia, ablation, electromagnetic, ultraosound, surface Plasmon resonance, biocompatibility.

<p> Nanoporous metal foams (NMFs), a relatively new class of materials with low&ndash; density, high surface area and conductivity, have been studied recently in nano science. These materials can be engineered to benefit many fields and promise to enable new technologies in areas such as hydrogen storage, high power density battery, surface&ndash;enhanced Raman spectroscopy and supercapacitors. Herein a new developed method is presented to synthesis low&ndash;density, nanoporous metal foams of silver and palladium. This study mainly focuses on the synthesis process of NMFs of and it also provides some new applications that are useful in research and daily life.</p><p> Silver NMFs were produced by mixing silver nitrate mixed with ethylene glycol, ethanol, and a reducing agent, and heating at 150 W for 5min using a CEM microwave. Higher conversions for this process were obtained using either hydrazine or sodium borohydride as the acceptable reducing agent for this redox reaction. Palladium NMFs were synthesized in the same way in the condition of 150 &deg;C with either hydrazine or sodium borohydride as the reducing agent.</p><p> Silver NMFs were applied in surface&ndash;enhanced Raman spectroscopy (SERS) as a substrate material. This material can enhance the detection of the rhodamine 6G (R6G), a model analyte. The limit of detection for rhodamine 6G was found to be 2 &times; 10^&ndash;6 M with the help of this silver nanoporous structure. Palladium NMFs was found to degrade methyl orange (MO). An aqueous MO solution will turn nearly colorless after only 10 h of mixing with 0.03g of palladium NMFs at room temperature under dark condition. Different concentrations of MO solution were also studied to compare the reaction rates. This application is applicable to the treatment of liquid waste and water purification and is thus conductive to improving the environment. </p><p>

<p> Externally bonded fiber-reinforced polymer (FRP) composites represent a simple and economical solution for many repair and strengthening applications in concrete structures. However, the potential occurrence of sudden and brittle debonding failure in such repairs becomes prominent when FRP-concrete bond undergoes environmental degradation induced by moisture. Ambient-cured low-viscosity Bisphenol A epoxy adhesives are most commonly utilized in the engineering practice to bond wet-layup FRP to the concrete substrate. This study aims to elucidate the effects of Bisphenol A-based epoxy modified with commercial surface-modified nanosilica (SMNS), core-shell rubber (CSR) nanoparticles and multi-walled carbon nanotubes (MWCNT) on the improvement of mechanical properties of the epoxy adhesives, and strength and durability of FRP-concrete adhesively bonded joints. Moisture ingress in epoxy, DSC, tensile test on epoxy and three-point bending beam bond tests were performed. To determine the effects of environmental degradation, all specimens were subjected to the following environments: control&mdash;23 &deg;C at RH 50 &plusmn; 10% for 18 weeks; and accelerated conditioning protocol (ACP)&mdash;water immersion at 45 &plusmn; 1 &deg;C for 18 weeks. Improvement in mechanical properties were observed in dogbone specimens modified with nanoparticles without any reduction in glass transition temperature (Tg). In control conditions, nanomodified epoxy groups exhibited enhanced mechanical properties compared to the neat epoxy. Following ACP, strength, elongation and modulus of elasticity of neat epoxy deteriorated significantly, while no significant deterioration was observed in the nanomodified group of adhesives. Among all the nanomodified adhesive groups CSR Type-1 showed most improvement in mechanical properties over neat epoxy group both in control condition and in ACP. CSR-modified adhesive joints experienced practically no degradation when subjected to ACP and showed the highest maximum bond strength retention of 100% among all the adhesive groups. The bond strength of neat epoxy adhesive joints degraded most dramatically (15%) following ACP.</p><p>

<p> The subject of extensive research has been the establishing of lower temperature soldering of electronic assemblies that are similar to the once common yet still preferred eutectic Tin-Lead (SnPb) soldering manufacturing processes that are below 217 &deg;C. This research opportunity will contribute data on mixed solder alloy assemblies that can be formed at lower process temperatures. There are many environmental and economic benefits of avoiding the current reliability concerns of assembling electronics at the standard high temperatures which peak at 230 &deg;C 260 &deg;C. To reduce this temperature the use of Bismuth containing solder pastes are mixing with the standard high temperature SAC solders for electronic assemblies. The materials evaluated are the (in weight percentages) 96.5Tin/3Silver/.5Copper (Sn/Ag/Cu) solder ball mixed with each solder paste, the eutectic 58Bismuth/42Tin (58Bi/42Sn), 57Bi/42Sn /1Ag and a propriety alloy that has a lower Bismuth content along with various micro alloys, 40-58Bi/Sn/X (X representing proprietary micro alloys or doping). In the assembly portion of this research the solder alloys were exposed to three different peak temperatures 180 &deg;C, 195 &deg;C, 205 &deg;C. Another reflow profile attribute of focus was times above 138 &deg;C the melting point of the eutectic Sn58Bi alloy. The ball and paste assembly portion of this research used the times above melting of 120sec and 240sec to represent process extremes and verify their significance on improving mixing level results. These times above melting did not consistently improve the mixing levels and therefore are not recommended or required during mixed low temperature solder assemblies. The results in this study suggest the recommended and optimum reflow profile to have a time above the melting point to be less than or equal to 90 seconds for mixed solder alloy assemblies in &ldquo;low&rdquo; (&lt; 200 &deg;C) peak temperature reflow oven profiles. This attribute ensures a reflow window similar to that of the eutectic SnPb processing. The second leg of this research was with a component assembly of a large ball grid array at the same various peak temperatures with a single time above 138 &deg;C, 90sec. This &ldquo;large&rdquo; (> 20mm a side) component is a SAC405 solder balled BGA with the dimensions of 42 &times; 28 &times; 0.8mm. With any large component the temperature gradient across the component is a risk factor and the results show that there are significantly differences of mixing from the center of the component to the edge due to an average 2.3 &deg;C temperature difference during convection reflow. The average mixing % levels recorded for T_peak= 180 &deg;C for the solder pastes with a 58Bi = 47%, 57Bi = 47% and 40-58Bi = 44%. The average mixing % levels recorded for T_peak= 195 &deg;C for the solder pastes with a 58Bi = 69%, 57Bi = 77% and 40-58Bi = 57%. The conclusions found also match previous work identifying the reflow peak temperatures remain a significant factor on the mixing %. This work&rsquo;s goal was to add to the knowledge of the electronics industry to better understanding the microstructure and mixing mechanisms of Bi/Sn/X-SAC solder joints for low temperature reflow assembly processes. </p><p>