Kenaf fiber is increasingly getting the attention of the industries due to its excellent mechanical properties, feasibility, growth rate, and ease of cultivation. On the other hand, cellulose nanofibril is one of the important building blocks of all the bast fibers which significantly contributes to their mechanical properties. However, most of the studies in the literature have estimated the value of axial elastic modulus for fiber-bundles which has some unavoidable issues resulting in incorrect modulus. Moreover, the transverse elastic modulus is another important parameter that also needs to be studied. Hence, to compensate for the gap in the literature, a single unit of both kenaf microfiber and cellulose nanofibril have been subjected to nanomechanical characterization to analyze their surface morphology and determine their elastic modulus in the axial and transverse direction. The experiments also pave to a protocol to characterize micro and nanofibrils nanomechanically and determine their elastic moduli.

The main goal of this project was to compare the changes in statistical variation and Weibull characteristics of the strength of glass rods as modified by heat treatment with and without an ion exchange bath. Several sample groups of 30 sodium borosilicate glass rod specimens were heat treated at various temperatures in air and in a potassium nitrate salt bath to induce an ion exchange process. All samples were then tested to failure in 4-point bending to assess the resulting Modulus of Rupture (MOR). Statistical analysis techniques and Weibull analysis were used to study the variations which occur within and between strength distributions of each sample group. A smaller sampling of test groups was subjected to fractographic analysis to study the effect of ion exchange on fracture features. The data shows that the ion exchange process caused a statistically significant increase in the strength of the glass rods. Samples which were heat treated do not show any significant changes in average strength. The fractographic analysis suggests that no changes in fracture morphology occurred as a result of ion exchange process, and that the critical flaw size population was not significantly different. / Master of Science

Silicon carbide is a useful monolithic and matrix ceramic due to its excellent mechanical properties and corrosion/oxidation resistance at high temperature. This makes it an attractive material for use in advanced applications, such as aircraft engines and high-speed flight. In this study, additively manufactured monolithic SiC and Cf/SiC CMCs, processed via direct ink writing (DIW) of a 53 vol% colloidal suspension, achieved >96% theoretical density through pressureless sintering. When present, fibers are aligned in the direction of the print path. Five different print paths were studied, including a 0o path, 90o path, 0/90o path, 0/15/30/45/60/75/90o path, and 0/30/60/90/60/30/0o path. Four-point bend testing was performed to determine flexural strength and Weibull analysis was performed. Strengths were highest for the 0o print path. The characteristic strength, σo, of this print path was 375 MPa with a Weibull modulus of 7.4 for monolithic SiC and a σo of 361 MPa with a Weibull modulus of 10.7 for Cf/SiC. Weibull modulus was greater for Cf/SiC samples compared to identically printed monolithic SiC samples. SEM and optical microscopy were used to analyze printed parts which showed a high degree of fiber alignment in the direction of the print. Fiber pullout was observed on the fracture surface, as well as intragranular fracture.

No description available.

Porous Wall Hollow Glass Microspheres (PWHGMs) were developed by the Savannah River National Laboratory. What makes these microspheres unique is the interconnected porosity spread throughout their wall allowing various materials to travel from the surface to the hollow interior. With their characteristic porosity, the PWHGMs are a great tool for encapsulating or filtrating different materials. Unfortunately, there is little information available on the mechanical properties of PWHGMs. The main goal of this research was to develop a method to crush individual microspheres and statistically analyze the results. One objective towards completing this goal was to measure the microsphere diameter distribution. Microsphere diameter is a major factor affecting strength as well as the Weibull parameters. Two different methods, microscopy counting and laser light scattering, used in the research yielded similar distributions. The main objective of this research was to analyze the crush strength of individual microspheres. Using nanoindentation, data were collected to analyze the crush strength of PWHGMs in uniaxial compression. Nanoindentation data were used to analyze how the strength of the PWHGMs changes through the different stages of production and at different diameter ranges. Data for 3M commercial microspheres were compared to ARC microspheres. Most data were analyzed using a statistical technique known as the two parameter Weibull analysis. The data indicated that the strength generally decreased as the microsphere diameter increased. Scattering in the data was nearly the same across all sample sets tested. Results indicated that the PWHGMs were weaker than the ARC hollow glass microspheres (HGMs). This is primarily due to the addition of wall porosity in the PWHGM. / Master of Science

Made available in DSpace on 2014-08-20T14:30:07Z (GMT). No. of bitstreams: 1 Dissertacao_cesar_henrique_zanchi.pdf: 490684 bytes, checksum: 7c7bf328a3f694acdaf1aad686b90d1e (MD5) Previous issue date: 2007-03-02 / The aim of this study was to evaluate the effect of additional etching with phosphoric acid at 35% in the bond strength and Weibull modulus of two adhesive systems applied to sound and affected dentin. Ninety human molars with coronal carious lesion were sectioned to produce flat coronal superficies with effected dentin surrounded by sound dentin, and allocated in six experimental groups: SB-CT: Single Bond® applied to manufacture s instructions; SB+15: Single Bond® with additional etching for 15s; SB+30: Single Bond® with additional etching for 30s; CF-CT: Clearfil SE Bond® applied to manufacture s instructions; CF+15: Clearfil SE Bond® with additional etching for 15s; CF+30: Clearfil SE Bond® with additional etching for 30s. Afterwards, the crowns were built up with a composite resin and, after 24h, mesiondistal sectioned to produce 2 or 3 slices in each substratum. Thereafter (24h), the slices were trimmed in hourglass shape and submitted to micro-tensile test (n=30). The data were analyzed by three-way ANOVA, Tukey s test (p<0,05) and Weibull analysis. The bond strength to affected dentin was significantly lower than sound dentin for the adhesives systems employed, save SB+30. The additional etching increased the bond strength to affected dentin. To sound dentin, the additional etching increased the bond strength for Clearfil SE Bond®, but decreased for Single Bond®. The Weibull modulus to affected dentin was lower for both adhesives systems. On sound dentin, Single Bond® showed lower Weibull modulus than Clearfil SE Bond® and the additional etching decrease this value. Although the additional etching may increase the bond strength to affected dentin, the means were lower than sound dentin, the same for Weibull modulus. The additional etching may reduce the bond strength and Weibull modulus for Single Bond® to sound dentin and, in opposite, increase for Clearfil SE Bond® / O objetivo deste estudo foi avaliar o efeito do condicionamento adicional com ácido fosfórico à 35% na resistência de união e módulo de Weibull de dois sistemas adesivos aplicados em dentina sadia e afetada por cárie. Noventa molares humanos com lesão cariosa oclusal foram desgastados produzindo superfícies oclusais planas, com DAC circundada por DS, e divididos em seis grupos experimentais: SBCT: Single Bond® aplicado conforme o fabricante; SB+15: Single Bond® com condicionamento ácido adicional de 15s; SB+30: Single Bond® com condicionamento ácido adicional 30s; CF-CT: Clearfil SE Bond® aplicado conforme o fabricante; CF+15: Clearfil SE Bond® com condicionamento ácido adicional de 15s; CF+30: Clearfil SE Bond® com condicionamento ácido adicional de 30s. Após, as coroas dos dentes foram restauradas em formato de bloco e, posteriormente (24h), seccionadas no sentido mésio-distal originando 2-3 fatias em cada substrato. Após 24h as fatias foram recortadas em formato de ampulheta e submetidas ao ensaio de microtração (n=30). Os valores de resistência de união foram analisados com ANOVA (3- fatores), teste de Tukey (p<0,05) e análise de Weibull. Em geral, a resistência de união foi significantemente menor em dentina afetada por cárie que em dentina sadia para ambos os sistemas adesivos, exceto para SB+30. O condicionamento ácido adicional resultou no aumento da resistência de união em dentina afetada por cárie. Em dentina sadia o condicionamento ácido adicional aumentou a resistência de união para o sistema Clearfil SE Bond®, mas reduziu para o sistema Single Bond®. O módulo de Weibull foi menor em dentina afetada por cárie para os dois sistemas adesivos. Em dentina sadia, Single Bond® apresentou menor módulo de Weibull que Clearfil SE Bond® e o condicionamento ácido adicional resultou na redução desse valor. Embora o condicionamento ácido adicional possa aumentar a resistência de união em dentina afetada por cárie, as médias foram menores que em dentina sadia, bem como o módulo de Weibull. O condicionamento ácido adicional 11 pode reduzir a resistência de união e o módulo de Weibull para Single Bond® em dentina sadia e, contrariamente, aumentar para o sistema Clearfil SE Bond®

In this Master Thesis work, the effect of pressure on sintering of cemented carbides is investigated. Special focus hasbeen given to the residual porosity after sintering. It is well known that sintering shrinkage depends on binder phasecontent, grain size, temperature and pressure. Thus 4 different cemented carbides grades were selected. The gradeswere pressed into standard products and TRS (Tensile Rupture Strength) rods with two different shrinkage factors.These were then sintered at different pressures and temperatures. Thereafter the impact of pressure on propertiessuch as Density, Coercivity, Porosity and TRS were analyzed. The observations were further supported with Weibullprobability analysis and fracture surface analysis in SEM.It has been shown that there exists a distinct threshold pressure at which significant reduction in porosity occurs forgiven compacted densities. For 3 out of 4 cemented carbide grades it has been observed that P2 sintering pressure issufficient to meet desired product characteristics. The fourth grade required a minimum sintering pressure of P4 toachieve desired quality criteria. Moreover it has been concluded that an increased sintering pressure increasesmaterial strength, as compared to vacuum sintering, thereby reducing the amount of early failures caused by poresduring TRS test.                                    Keywords: Cemented Carbides, Pressurized Sintering, Tungsten carbide, Porosity, Vacuum sintering, TensileRupture Strength, Weibull analysis, Fracture surface analysis.

Capítulo 1. Objetivos: Medir e comparar o perfil de tensão residual da cerâmica de recobrimento aplicada sobre infraestruturas em zircônia tetragonal policristalina estabilizada por ítria (Y-TZP), em um compósito de alumina/zircônia (ZTA) e em uma alumina policristalina (AL). Material e Métodos: Os perfis de tensão residual de cada um dos materiais foi medido por meio do método \"hole-drilling\" em discos de 19 mm de diâmetro e 2,2 mm de espessura (0,7 mm de infraestrutura + 1,5 mm de porcelana de cobertura) .Resultados: Os espécimes de AL exibiram tensões de compressão que aumentaram numericamente com a profundidade, enquanto que as tensões compressivas mudaram para tensões de tração no interior das amostras de Y-TZP. As amostras de ZTA exibiram tensões de compressão na superfície, decrescendo com a profundidade até 0,6 mm, tornando-se compressivas novamente próximo à infraestrutura. Conclusão: O ZTA não apresentou tensões de tração em nenhum ponto ao longo da espessura da cerâmica de recobrimento. A AL apresentou um perfil de tensão residual mais favorável, gerado pelas tensões compressivas. A Y-TZP apresentou o perfil mais desfavorável, por apresentar tensões de tração próximo à infraestrutura. Capítulo 2. Objetivos: 1) Comparar os coeficientes de susceptibilidade ao crescimento subcrítico (n), de uma zircônia tetragonal policristalina estabilizada por ítria, obtidos por meio de dois ensaios de fadiga: cíclica e dinâmica. 2) Verificar o efeito da frequência usada no ensaio de fadiga cíclica no tempo de vida característico. Material e Métodos: Espécimes em forma de barras (25 mm x 4 mm x 3 mm) foram confeccionadas de acordo com as recomendações do fabricante. Os ensaios de fadiga dinâmica (n=70) e de fadiga cíclica (n=75) foram realizados por meio de resistência à flexão em quatro pontos para a obtenção dos parâmetros de crescimento de trincas subcrítico (SCG). O ensaio de fadiga cíclica também foi realizado em duas frequências (2 e 10 Hz), utilizando valores de tensão máxima entre 350 e 600 MPa. Todos os espécimes fraturados foram inspecionados em microscópio eletrônico de varredura para que fosse identificada a origem da fratura. Os dados de fadiga dinâmica foram analisados por meio das fórmulas apresentadas na ASTM C 1368-00. Os dados de fadiga cíclica foram analisados por meio da estatística de Weibull e por meio de análise tipo \"General Log Linear Model\". Resultados: A Y-TZP apresentou valores dos parâmetros de SCG obtidos no ensaio de fadiga dinâmica de ?fo = 667 MPa e n = 54. Os parâmetros de Weibull obtidos a partir dos resultados do mesmo ensaio foram de m = 7,9, ?0 = 968,9 MPa e ?5% = 767 MPa. Os parâmetros de Weibull obtidos no ensaio de fadiga cíclica foram estatisticamente semelhantes para as duas frequências utilizadas, o m* foi de 0,17 para 2Hz e de 0,21 10Hz; os tempos de vida característicos (?, em número de ciclos) foram de 1,93 x 106 e 40.768, respectivamente para 2 e 10 Hz. O valor de n obtido na fadiga cíclica foi de 48 e 40, nas frequências de 2 e 10 Hz, respectivamente. Não foi observado o efeito da frequência da aplicação da tensão, do nível de tensão, nem da interação dos dois no tempo de vida da Y-TZP, quando analisados pelo General Log Linear Model. Conclusão: Os coeficientes de susceptibilidade ao crescimento subcrítico (n) obtidos por meio de fadiga cíclica e dinâmica foram semelhantes para a Y-TZP testada. Os extensos intervalos de confiança obtidos nos ensaios de fadiga cíclica indicaram não haver efeito da frequência usado nesse método de fadiga nos tempos de vida característicos da Y-TZP testada. / Chapter 1. Objective: was: to measure and compare the residual stress profile in the veneering ceramic layered on three different polycrystalline ceramic frame-work materials: Y-TZP, alumina polycrystalline (AL) and zirconia toughened alumina (ZTA).Materials and Methods. The stress profile was measured with the hole-drilling method in bilayered disk samples of 19 mm diameter with a 0.7 mm thick Y-TZP, AL or ZTA framework and a 1.5 mm thick layer of the corresponding veneering ceramic. Results: The AL samples exhibited increasing compressive stresses with depth, while compressive stresses switching into interior tensile stresses were measured in Y-TZP samples. ZTA samples exhibited compressive stress at the ceramic surface, decreasing with depth up to 0.6 mm from the surface, and then becoming compressive again near the framework. Conclusions: Y-TZP samples exhibited a less favorable stress profile than those of AL and ZTA samples. Chapter 2. Objectives: 1) To compare the stress corrosion coefficient (n) of a Y-TZP, obtained by two fatigue tests: cyclic and dynamic and 2) Evaluate the effect of frequency used in the cyclic fatigue test in the characteristic lifetime. Methods: Bar shaped specimens (4 mm x 25 mm x 3 mm) were prepared according to the manufacturer\'s recommendations. The dynamic fatigue test (n = 70) and cyclic fatigue (n = 75) were performed by four-point bending to obtain the slow crack growth parameters (n) .The cyclic fatigue test was also conducted in two frequencies (2 and 10Hz), using stress levels between 350 and 600 MPa. All fractured specimens were inspected by SEM so that the origin of the fracture were identified. The dynamic fatigue data were analyzed using the formulas given in ASTM C 1368-00. Cyclic fatigue data were analyzed using Weibull statistics and by the Log General Linear Model. Results: The material showed values of parameters obtained in the SCG assay dynamic fatigue ?fo = 667 and n = 54. The Weibull parameters obtained from the same test results were m = 7.9, ?0 = 968, 9 and ?5% = 767. The Weibull parameters obtained by cyclic fatigue were statistically similar for the two frequencies used, the m* was 0.17 (2 Hz) and 0.21 (10 Hz); characteristic lifetimes (?) were 1.93 x 106 and 40768, respectively. The n value obtained by cyclic fatigue was 48 and 40 at frequencies of 2 and 10 Hz, respectively. There was no effect of the frequency, the stress level or the interaction of the two in the Y-TZP lifetime, when analyzed by General Log Linear Model. Conclusion: The n values obtained by cyclic and dynamic fatigue tests were similar to Y-TZP tested. The extensive confidence intervals obtained in cyclic fatigue tests showed no effect of frequency used this method in fatigue characteristic lifetimes of the Y-TZP tested.

The main goal of this diploma thesis "IT systems reliability analysis" is to analyse and suggest the best PC component seller according to criterion of minimum costs for guarantee services. Theoretical part deals with general importance of technical systems reliability and brings methodological basis for reliability analysis and describes methods and ways how to increase reliability in practise. Following part is focused on identification computer most critical component through Failure Tree Analysis method and modelling its failure-free time by using Weibull analysis. On the base of maintenance costs analysis was chosen the most appropriate distributor.

Capítulo 1. Objetivos: Medir e comparar o perfil de tensão residual da cerâmica de recobrimento aplicada sobre infraestruturas em zircônia tetragonal policristalina estabilizada por ítria (Y-TZP), em um compósito de alumina/zircônia (ZTA) e em uma alumina policristalina (AL). Material e Métodos: Os perfis de tensão residual de cada um dos materiais foi medido por meio do método \"hole-drilling\" em discos de 19 mm de diâmetro e 2,2 mm de espessura (0,7 mm de infraestrutura + 1,5 mm de porcelana de cobertura) .Resultados: Os espécimes de AL exibiram tensões de compressão que aumentaram numericamente com a profundidade, enquanto que as tensões compressivas mudaram para tensões de tração no interior das amostras de Y-TZP. As amostras de ZTA exibiram tensões de compressão na superfície, decrescendo com a profundidade até 0,6 mm, tornando-se compressivas novamente próximo à infraestrutura. Conclusão: O ZTA não apresentou tensões de tração em nenhum ponto ao longo da espessura da cerâmica de recobrimento. A AL apresentou um perfil de tensão residual mais favorável, gerado pelas tensões compressivas. A Y-TZP apresentou o perfil mais desfavorável, por apresentar tensões de tração próximo à infraestrutura. Capítulo 2. Objetivos: 1) Comparar os coeficientes de susceptibilidade ao crescimento subcrítico (n), de uma zircônia tetragonal policristalina estabilizada por ítria, obtidos por meio de dois ensaios de fadiga: cíclica e dinâmica. 2) Verificar o efeito da frequência usada no ensaio de fadiga cíclica no tempo de vida característico. Material e Métodos: Espécimes em forma de barras (25 mm x 4 mm x 3 mm) foram confeccionadas de acordo com as recomendações do fabricante. Os ensaios de fadiga dinâmica (n=70) e de fadiga cíclica (n=75) foram realizados por meio de resistência à flexão em quatro pontos para a obtenção dos parâmetros de crescimento de trincas subcrítico (SCG). O ensaio de fadiga cíclica também foi realizado em duas frequências (2 e 10 Hz), utilizando valores de tensão máxima entre 350 e 600 MPa. Todos os espécimes fraturados foram inspecionados em microscópio eletrônico de varredura para que fosse identificada a origem da fratura. Os dados de fadiga dinâmica foram analisados por meio das fórmulas apresentadas na ASTM C 1368-00. Os dados de fadiga cíclica foram analisados por meio da estatística de Weibull e por meio de análise tipo \"General Log Linear Model\". Resultados: A Y-TZP apresentou valores dos parâmetros de SCG obtidos no ensaio de fadiga dinâmica de ?fo = 667 MPa e n = 54. Os parâmetros de Weibull obtidos a partir dos resultados do mesmo ensaio foram de m = 7,9, ?0 = 968,9 MPa e ?5% = 767 MPa. Os parâmetros de Weibull obtidos no ensaio de fadiga cíclica foram estatisticamente semelhantes para as duas frequências utilizadas, o m* foi de 0,17 para 2Hz e de 0,21 10Hz; os tempos de vida característicos (?, em número de ciclos) foram de 1,93 x 106 e 40.768, respectivamente para 2 e 10 Hz. O valor de n obtido na fadiga cíclica foi de 48 e 40, nas frequências de 2 e 10 Hz, respectivamente. Não foi observado o efeito da frequência da aplicação da tensão, do nível de tensão, nem da interação dos dois no tempo de vida da Y-TZP, quando analisados pelo General Log Linear Model. Conclusão: Os coeficientes de susceptibilidade ao crescimento subcrítico (n) obtidos por meio de fadiga cíclica e dinâmica foram semelhantes para a Y-TZP testada. Os extensos intervalos de confiança obtidos nos ensaios de fadiga cíclica indicaram não haver efeito da frequência usado nesse método de fadiga nos tempos de vida característicos da Y-TZP testada. / Chapter 1. Objective: was: to measure and compare the residual stress profile in the veneering ceramic layered on three different polycrystalline ceramic frame-work materials: Y-TZP, alumina polycrystalline (AL) and zirconia toughened alumina (ZTA).Materials and Methods. The stress profile was measured with the hole-drilling method in bilayered disk samples of 19 mm diameter with a 0.7 mm thick Y-TZP, AL or ZTA framework and a 1.5 mm thick layer of the corresponding veneering ceramic. Results: The AL samples exhibited increasing compressive stresses with depth, while compressive stresses switching into interior tensile stresses were measured in Y-TZP samples. ZTA samples exhibited compressive stress at the ceramic surface, decreasing with depth up to 0.6 mm from the surface, and then becoming compressive again near the framework. Conclusions: Y-TZP samples exhibited a less favorable stress profile than those of AL and ZTA samples. Chapter 2. Objectives: 1) To compare the stress corrosion coefficient (n) of a Y-TZP, obtained by two fatigue tests: cyclic and dynamic and 2) Evaluate the effect of frequency used in the cyclic fatigue test in the characteristic lifetime. Methods: Bar shaped specimens (4 mm x 25 mm x 3 mm) were prepared according to the manufacturer\'s recommendations. The dynamic fatigue test (n = 70) and cyclic fatigue (n = 75) were performed by four-point bending to obtain the slow crack growth parameters (n) .The cyclic fatigue test was also conducted in two frequencies (2 and 10Hz), using stress levels between 350 and 600 MPa. All fractured specimens were inspected by SEM so that the origin of the fracture were identified. The dynamic fatigue data were analyzed using the formulas given in ASTM C 1368-00. Cyclic fatigue data were analyzed using Weibull statistics and by the Log General Linear Model. Results: The material showed values of parameters obtained in the SCG assay dynamic fatigue ?fo = 667 and n = 54. The Weibull parameters obtained from the same test results were m = 7.9, ?0 = 968, 9 and ?5% = 767. The Weibull parameters obtained by cyclic fatigue were statistically similar for the two frequencies used, the m* was 0.17 (2 Hz) and 0.21 (10 Hz); characteristic lifetimes (?) were 1.93 x 106 and 40768, respectively. The n value obtained by cyclic fatigue was 48 and 40 at frequencies of 2 and 10 Hz, respectively. There was no effect of the frequency, the stress level or the interaction of the two in the Y-TZP lifetime, when analyzed by General Log Linear Model. Conclusion: The n values obtained by cyclic and dynamic fatigue tests were similar to Y-TZP tested. The extensive confidence intervals obtained in cyclic fatigue tests showed no effect of frequency used this method in fatigue characteristic lifetimes of the Y-TZP tested.