Thesis (PH. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 173-184). Also available on the World Wide Web.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 241-254). Also available via the Internet.

Report (M. Engr.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaf 26). Also available via the Internet.

Made available in DSpace on 2014-06-11T19:27:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-08Bitstream added on 2014-06-13T19:47:37Z : No. of bitstreams: 1 brocks_t_me_guara.pdf: 1127902 bytes, checksum: d3d7631f1ee3c081efb6530997375ebd (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A indústria aeronáutica nacional tem intensificado sua busca por materiais alternativos, com características e propriedades que permitam a substituição segura do material metálico. Com o objetivo de ganhar competitividade no mercado internacional e contribuir para o desenvolvimento tecnológico no país, o presente trabalho apresenta a técnica de processamento de moldagem por transferência de resina (RTM), utilizada na fabricação de materiais compósitos estruturais e ainda pouco estudada no Brasil. Os compósitos processados por essa técnica apresentam maior fração volumétrica de fibras, melhor acabamento superficial e pouca ou nenhuma necessidade de acabamento do componente produzido. Este trabalho compreende o processamento e a caracterização de compósitos produzidos com resina epóxi monocomponente Cycom 890 e dois tipos de tecidos, plain weave e twill 2x2, ambos de fibra de carbono. Para a determinação dos parâmetros de processamento, a resina foi caracterizada quanto aos seus comportamentos térmico e viscoso. Com base nos resultados e testes preliminares foi determinada a temperatura mais adequada de injeção em 100°C, a pressão de injeção entre 0,2 e 0,4 MPa e de vácuo em 250 mPa.s. Os compósitos produzidos foram analisados pela técnica de ultrassom C-Scan e os resultados mostraram que os laminados processados estão homogêneos quanto à impregnação. Testes de tração mostram que os laminados com tecido tipo Twill apresentam maior média de resistência à tração, enquanto que a diferença de trama não influencia significativamente às propriedades de flexão e cisalhamento, que se mostraram superiores as propriedades de compósitos produzidos em autoclave com maiores porcentagens de reforço. Em fadiga, ambos os laminados apresentaram um curto intervalo, com tensões próximas à de tração, no entanto, o laminado PW/Cycom apresentou maior... / The national aeronautical industry has intensified your search for alternative materials, with characteristics and properties that allow the safety replacement of metallic material. The goal is to gain competitiveness on international market and contribute with technological development in the country. This work presents a processing technique of resin transfer molding (RTM), used on manufacture of structural composites and understudied in Brazil. Composites processed by this method have a higher fibers volume fraction, better surface finish and little or no finishing require of produced component. This work includes the processing and characterization of composites made with monocomponent epoxy resin Cycon 890 and two types of carbon fiber fabrics, plain weave and twill 2x2. To determine processing parameters, the resin was characterized regarding thermal behavior and viscosity. Based on this results and preliminary tests, it was determined the most appropiate injection temperature at 100°C, the injection pressure between 0.2 and 0.4 MPa and vacuum pressure in 250 mPa.s. Composites produced were analyzed by C-scan ultrasound technique showing a homogeneous impregnation of processed panels. Tensile and flexural tests characterized mechanically composites, allowing seeing that Twill fabric has higher medium tensile performance, while the difference of weft does not influence significantly the flexural and shear properties, that are superior than properties of composites made by autoclaving with higher reinforced volume. In fatigue, both composites showed short interval, close to ultimate tensile strength (uts), however, the PW/Cycom laminated showed higher fatigue resistance, with an interval between 85-92% of uts. About the thermal behavior, it was observed an improvement in properties with the addition of carbon... (Complete abstract click electronic access below)

OBJECTIVES: Fiber-reinforced composite has been commercialized as universal and flowable resin based composite. The objective of this study is to test and compare fracture toughness of fiber-reinforced composite resins to conventional particulate filler composite resins. MATERIALS AND METHODS: Four products were tested in this study, including: GC everX Posterior (EXP), 3M ESPE Filtek Supreme Ultra Universal (FSU), 3M ESPE Filtek Supreme Ultra Flowable (FSF), Nanova Biomaterials NovaPro Flowable (NPF), Nanova Biomaterials NovaPro Universal (NPU), Prime Dental Manufacturing Prime­ dent flowable (PDF). NovaPro contains hydroxyapatite nanofiber as filler and everX has glass fiber as filler. Materials were tested by creating specimens in two configurations using metallic molds (n=5 or 10/group). Flexural toughness specimens were rectangles 2.5×5×25mm with a slot and V­notch of 1x2.4mm with at the central edge. All specimens were made following manufacturer’s instructions under 1,470mW/cm2 light curing. After setting and de­molding, specimens were kept in 37oC water for 72 hours. Testing was performed on an Instron machine (Model 5566A) with a three-point bending fixture at a cross­head speed of 0.25 mm/sec and V­notch faced to tensile side. One­way ANOVA post hoc Tukey HST (JMP Pro 12.0.) was used for data analysis (significance level = 0.05). RESULTS: Fracture toughness results are shown in Table 1. There was significant difference among groups. CONCLUSIONS: Composites with fiber fillers showed significant higher fracture toughness. / 2020-07-23T00:00:00Z

Modulus reduction and damage accumulation during fatigue cycling of an injection moulded composite been studied. The material is a long, discontinuous glass fibre reinforced nylon composite having a skin/core structure. A continual decrease in modulus with cycling is observed for composite and single skin layer specimens. During fatigue cycling of composite specimens damage accumulates in both the skin and core layers and both layers contribute to the measured modulus reduction. Damage accumulation in the core, in the form of transverse cracks, is studied in detail. These cracks initiate predominantly at the free edges and grow across the specimen width with cycling. A milling/dye penetrant technique is developed to quantify the cracking and average crack spacings are related to measured modulus reductions at a range of peak stresses. The experimental data is compared with predictions made using a shear-lag model developed for continuous fibre cross-ply laminates relating modulus reduction to average crack spacing. A theoretical model, based on the Cox model, is derived to predict modulus reduction/cycling curves for skin layer specimens. Cracking patterns in the core are predicted using a strain energy release rate approach which is compared with experimental data. Empirical relationships, derived for the modulus reduction of the skin and core layers are combined to predict modulus reduction/cycling curves at a range of specimen widths and stress levels.

Attempts have been made to synthesise a novel siloxane-containing dicyanate ester, 1,3-bis(4-cyanatophenyl)-1,1,3,3-tetramethyldisiloxane, commencing from 4-bromophenol or 4-methoxyphenol. Most of these syntheses have involved the use of a Grignard reaction to form a disiloxane group, followed up subsequent cleavage of an alkyl-protecting group to yield a free phenol. Several different ethers have been attempted, but none was successful. The extreme susceptibility of the aryl silicon-carbon bond to cleavage under acidic conditions has been demonstrated by these reactions. A novel phosphazene-containing dicyanate ester, 1,3-bis(4-cyanatophenyl)-1,3,5,5-tetraphenoxycyclotriphosphazene has been successfully synthesised in a four-step procedure with an overall yield of ca. 35%. The cyanate ester has been characterised by differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, thermomechanical analysis (TMA), 1H, 13C and 13P NMR spectroscopy, and Fourier-Transform Infra-red (FT-IR) and Raman spectroscopy. The thermal data collected showed a surprisingly low glass transition temperature (59 °C) and enthalpy of polymerisation (ca. 36-5 kJ mol-1 of cyanate). The former figure was confirmed by TMA and modulated DSC. However, the cured cyanate showed reasonably high thermal stability: no mass loss was observed before 300 °C. Total decomposition did not occur until about 650 °C.

In this work an attempt has been made to develop theories for finite element static and dynamic stress analysis tailored for use with composite layered plates and shells in this way it was hoped to provide accurate values of the stresses particularly transverse shear stresses through the thickness, and to perform accurate natural frequency analysis by including non-linear effects such as centrifugal stiffening. Initial derivations were based upon first order facet shell element analysis and first order curved shell element analysis. Subsequently, derivations were produced for higher order element analysis. A programming package has been developed based upon the above derivations, and containing a banded solver as well as a frontal solver, capable of analysing structures build up from uniform or variable thickness layers and with a multiple number of layers having constant or variable dimension. Results obtained with the aid of the present package have been compared with results derived from experimental work as well as with results derived from available analytical solutions. Investigations have been carried out for existing compressor blades, made of isotropic material and layered composite material, respectively. The results obtained from the package have been compared with available experimental results produced by RR or carried out at Cranfield. It has been shown that the above mentioned derivations produce comparable results and the package has proved to be reliable and accurate.

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Made available in DSpace on 2014-10-09T12:40:48Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:08Z (GMT). No. of bitstreams: 1 02945.pdf: 7569040 bytes, checksum: 02354504530dda19f3da88d601d653f1 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP