Made available in DSpace on 2014-06-11T19:27:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-08Bitstream added on 2014-06-13T20:16:13Z : No. of bitstreams: 1 caltabiano_pcro_me_guara_prot.pdf: 15712359 bytes, checksum: c76e08dd6fa7273cb27b89a44031baaa (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Fracture surface express the sequence of energy release events during crack propagation and, in the case of metallic alloys, the topographic evolution can descrbr the action of load lines, failures due to using processing, and others. In the cases, the quantitative fractography can help the investigation of failures in structures and manufacturing processes. In this work, two correlation analyses were carried out: the first between the stretch zone width (SZW) and fracture toughness (Kc) and the second between Kc and the fractality of the fractured surface topography, both analyzed by digital image processing. The 15-5PH stee and AA7475 aluminium alloy fracture surfaces for analysis were obtained by toughness testing. Each seurface was mapped by extend depth of field technique, and the following fractal dimension values were calculated for each mapped position: monofractal dimension (Df), structural dimension (Ds) and textural dimension (DT). The results for analysis between LZE and Kc data showed a high correlation for 15-5PH steel, also checking the validity of the delimitation method of SZW and the image reconstruction process. The fractal analysis showed that as higher the ductility of the material, as lower will be the level of linear correlation obtained between toughness and the fractal values. However, for 15-5PH steel, with behavior ranging between the linear-elastic and elastic-plastic, the level of linear correlation between Kc and the fractal values tend to be significant, especially for established correlations involving the textural dimension (Dt). However, for AA 7475 aluminium alloy no significant correlation could be established due to predominance of shallow dimples

Orientador: Luis Rogério de Oliveira Hein / Banca: Alfeu Saraiva Ramos / Banca: Miriam de Lourdes N. Motta Melo / Resumo:Superfícies de fratura expressam a sequência de eventos de liberação de energia coma propagação de trincas. No caso de ligas metálicas, a evolução das formações topográficas pode indicar as linhas de ação de carga, falhas de uso ou de processamento e outros. Nestes casos, a fractografia pode auxiliar na investigação de falhas estruturais e nos processos de manufatura. Neste trabalho foram realizados dois tipos de análise de correlações: a primeira entre a largura da zona deestiramento (LZE) e o valor da tenacidade a fratura (Kc) e a segunda entre os valores de tenacidade à fratura e a fractalidade da topografia das superfícies fraturadas, sempre por meio de processamento digital de imagens. Para obtenção das superfícies de fratura dos corpos de provas do aço 15-5PH e da liga do alumínio AA 7475, este foram ensaiados para obtenção de valores de Kic. As superfícies de fratura geradas foram mapeadas pela técnica de reconstrução por extensão de foco, e para cada região foram calculados os valores de dimensão fractal: dimensão monofractal (Df), dimensão estrutural (Ds) e dimensão textural (DT). Os resultados da análise entre LZE e Kc apresentaram uma alta correlação para o aço 15-5PH, mostrando a validade do método de seleção da LZE o do processo de reconstrução da imagem. Já análise fractal mostrou quanto maior a ductilidade do material menor é o nível de correlação linear obtido entre tenacidade e os valores fractais. Contudo, para o aço 15-5PH, com comportamento transitando entre o regime linear elástico e elasto-plástico, o nível da correlação linear entre Kc e os valores fractais tende a ser significante, principalmente para as correlações estabelecidas envolvendo a dimensão textural (DT). Devido ao caráte dúctil da liga AA 7475 não foram encontrados correlações significantes / Abstract: Fracture surface express the sequence of energy release events during crack propagation and, in the case of metallic alloys, the topographic evolution can descrbr the action of load lines, failures due to using processing, and others. In the cases, the quantitative fractography can help the investigation of failures in structures and manufacturing processes. In this work, two correlation analyses were carried out: the first between the stretch zone width (SZW) and fracture toughness (Kc) and the second between Kc and the fractality of the fractured surface topography, both analyzed by digital image processing. The 15-5PH stee and AA7475 aluminium alloy fracture surfaces for analysis were obtained by toughness testing. Each seurface was mapped by extend depth of field technique, and the following fractal dimension values were calculated for each mapped position: monofractal dimension (Df), structural dimension (Ds) and textural dimension (DT). The results for analysis between LZE and Kc data showed a high correlation for 15-5PH steel, also checking the validity of the delimitation method of SZW and the image reconstruction process. The fractal analysis showed that as higher the ductility of the material, as lower will be the level of linear correlation obtained between toughness and the fractal values. However, for 15-5PH steel, with behavior ranging between the linear-elastic and elastic-plastic, the level of linear correlation between Kc and the fractal values tend to be significant, especially for established correlations involving the textural dimension (Dt). However, for AA 7475 aluminium alloy no significant correlation could be established due to predominance of shallow dimples / Mestre

Orientador: Alvaro Della Bona, Altair A. Del Bel Cury / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-04T13:44:44Z (GMT). No. of bitstreams: 1 Boscato_Noeli_D.pdf: 1647960 bytes, checksum: 3d012e02dce78a5277da1ede4cc574e4 (MD5) Previous issue date: 2005 / Resumo: Este estudo avaliou o efeito do tratamento de superfície na resistência adesiva à tração (s) entre resina e as cerâmicas IPS Empress®(E1) e VITAVM7®(V7) e o modo de falha nessa interface adesiva. A metodologia proposta teve por finalidade testar a hipótese de que a s entre resina e cerâmica é controlada pelo tratamento de superfície das cerâmicas. Foram confeccionados 10 blocos de uma cerâmica a base de leucita, (E1) e de uma cerâmica feldspática com duas fases vítreas (V7), que foram polidos até a granulação de 1 µm. Os blocos de cada cerâmica foram divididos aleatoriamente em dois grupos e tiveram suas superfícies tratadas como segue (n=5): Grupos E1HF e V7HF: aplicação de ácido hidrofluorídrico a 9,5% (HF - Ultradent) aplicado por 60 s; Grupos E1CS e V7CS: jateamento com partículas de alumina modificadas por sílica (CS ¿ Cojet System, 3M-Espe), aplicado por 15 s. As superfícies cerâmicas tratadas foram lavadas, secadas e o silano foi aplicado deixando-o evaporar. Aplicaram-se duas camadas finas de adesivo (Single Bond, 3M), seguido da aplicação de camadas de 2 mm de resina composta (Z250, 3M), que foram fotopolimerizadas durante 40 s cada uma. Os blocos cerâmica-adesivo-resina composta foram seccionados em dois eixos, x e y, obtendo-se corpos-de-prova em forma de barras (n=30), com área adesiva média de 1,04 mm2. Os corpos-de-prova foram armazenados em água destilada a 37°C por uma semana antes do teste de tração em uma máquina de ensaios universal com velocidade de carga de 1.0 mm.min-1, seguido da análise microscópica da superfície fraturada. A análise estatística foi realizada pela análise de variância, teste de Tukey (a=.01) e análise de Weibull. As médias e desvio padrão da s (MPa) foram: E1HF: 29,8±4,5(a); E1CS: 24,6±5,6(b); V7HF: 22,3±4,0(b); V7CS: 15,7±6,9(c). Os valores médios de s do Grupo E1HF foram significativamente maiores que os valores médios dos demais grupos (p=0,0001). As duas cerâmicas apresentaram valores médios de s significativamente maiores quando tratadas com HF do que com CS (p=0,0001). Todas as fraturas ocorreram dentro da zona adesiva. O módulo de Weibull (m) foi mais alto para o Grupo E1HF (7,66), e o Grupo V7CS mostrou o valor mais baixo de m (2,54). Os resultados confirmam a hipótese inicial de que a s da resina à cerâmica é controlada, primariamente, pelo tratamento de superfície do material cerâmico / Abstract: This study evaluated the effect of ceramic surface treatments on tensile bond strength (s) and the mode of failure of a resin bonded to two types of ceramics, testing the hypothesis that s of ceramics to resin is controlled by the ceramic surface treatment. Methods: Ten blocks of each the hot-pressed leucite-based ceramic (E1- IPS Empress) and the two-phase glassy feldspathic ceramic (V7-VITAVM7) were fabricated, polished through 1 µm alumina abrasive, and divided into two groups per ceramic (n=5): Groups E1HF and V7HF, 9.5% hydrofluoric acid (HF) was applied for 60 s; Groups E1CS e V7CS, silica coating (CS) using Cojet System (3M-Espe) for 15 s. The treated ceramic surfaces were washed and dried. Silane was applied and let to evaporate. An adhesive resin (Single Bond, 3M) followed by a resin composite (Z250, 3M) were applied on the ceramic treated surfaces and light cured. The composite-ceramic blocks were cut to produce bar-shaped specimens with a mean bonding area of 1.04 mm2 (n=30). Specimens were stored in 37°C distilled water for 1 week before tensile loading to failure in a universal testing machine with cross-head speed of 1.0 mm.min-1. Fracture surfaces were examined under scanning electron microscope (SEM). Results were statistically analyzed using one way ANOVA, Tukey¿s test and Weibull analyses. Results: Mean s and standard deviation (MPa) values were as follows: E1HF: 29.8±4.5(a); E1CS: 24.6±5.6(b); V7HF: 22.3±4.0(b); V7CS: 15.7±6.9(c). Mean s value of Group E1HF was statistically higher than the other Groups mean values (p=0.0001). HF treatment produced significantly higher mean s value than CS treatment, independent of the ceramic material (p=0.0001). All fractures occurred within the adhesion zone. E1HF showed the highest Weibull modulus (m) value (7.66) and V7CS exhibited the lowest m value (2.54). Conclusion: Results confirmed the testing hypothesis that s of ceramics to resin is controlled primarily by the ceramic surface treatment / Doutorado / Protese Dental / Doutor em Clínica Odontológica

No description available.

The single crystal superalloy PWA 1484 is used in hot section turbine blade applications due to its performance at high temperatures. In practice, the turbine blades are often coated in order to protect them from environmental degradation. However, under repeated cyclic loading, the coating may serve as a site for crack initiation in the blades. Fundamental out-of-phase (OP) thermo-mechanical fatigue (TMF) studies, primarily using uncoated solid cylindrical test samples, have previously examined both crack initiation and propagation in PWA 1484. In this work, mechanical strain-controlled OP TMF tests were performed on coated and uncoated specimens of a hollow cylindrical geometry in order to study the effects of both geometry and coating on the TMF crack initiation behavior. To accomplish this, it was necessary to create and analyze a modified gripping mechanism due to the unique geometry of the test samples, and as predicted by hand calculations and finite element analysis, these modifications proved to be successful. The TMF test results for the uncoated material were compared to those from previous studies under the same testing conditions, and it was found that the differences in geometry had a minimal impact on fatigue life. Comparisons of the results for the coated and uncoated material suggested that the coating may have offered a slight improvement in life, although insufficient results were available to determine whether these differences were statistically significant. Damage mechanisms resulting from different test conditions were also observed through microscopy on failed specimens.

Made available in DSpace on 2014-06-11T19:27:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-01-26Bitstream added on 2014-06-13T20:16:13Z : No. of bitstreams: 1 marques_tpz_me_guara.pdf: 7111627 bytes, checksum: 6e3208be9c6bd1d049644a4aa33de525 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Superfícies de fratura apresentam a evolução entrópica durante a propagação de trincas, demonstrando relações entre componentes estruturais, campos de tensões locais e formações típicas de relevo. No caso das ligas metálicas, a evolução das formações topográficas pode indicar as linhas de ação de carga, a dinâmica do processo de fratura, falhas de uso ou de processamento, e outros. Neste trabalho, foram realizadas análises da relação entre a dimensão fractal e a variação do fator intensidade de tensão, da relação entre a dimensão fractal e a posição à frente da trinca, além do estudo da influência da espessura nos valores de dimensão fractal. Esses estudos foram efetuados a partir da topografia das superfícies fraturadas do aço 15-5PH obtidas em ensaios de propagação de trincas por fadiga, conforme ASTM E647. A investigação das fraturas foi feita por meio do método de reconstrução por extensão de foco, com o qual foi possível calcular os valores de dimensão monofractal (Df), dimensão textural (Dt) e dimensão estrutural (Ds), utilizando os mapas de elevações gerados pelo método. Os resultados das análises mostraram que os valores de Ds foram sensíveis à mudança dos micromecanismos de fratura, sendo que eles aumentaram até a transição do estágio II para o estágio III, sofrendo uma leve queda quando a trinca se propagava de forma instável e, em seguida, voltaram a aumentar quando a trinca estava perto de atingir seu tamanho crítico. Também foi observado que os valores de Ds e Dt se comportaram de forma inversa com o aumento da velocidade de propagação da trinca, em que os valores de Ds aumentaram e os de Dt decresceram em relação à evolução de K. Sendo, então, a dimensão estrutural responsável por descrever o comportamento anisotrópico do relevo, devido à evolução... / Fracture surfaces present the entropic evolution during the crack propagation, demonstrating relationship between structural components, local stress fields and typical relief formation. Regarding metallic alloys, the evolution of topographical formations may indicate the load action lines, the dynamism of the fracture process, during the processing or in use failures. In this work, it was performed the analysis of the relation between the fractal dimension and the stress intensity factor deviation, the relation between the fractal dimension and the crack tip position and also the study of the thickness influence in the fractal dimension values. These studies were performed by means of the topography of the 15-5PH steel fracture surfaces obtained throughout the fatigue crack propagation tests, in accordance with ASTM E647. The fractures investigation was executed using the 3-D reconstruction by extended depth of field method, allowing the possibility to calculate the values of the monofractal dimension (Df), textural dimension (Dt) and structural dimension (Ds), using of the elevation maps generated by the method. The analysis results showed that Ds was sensitive to changes on fracture micromechanisms, once they have increased up to the stage II to stage III transition, appearing a smooth reduction during the crack propagation at the unstable region and, after this, the values turned back to increase when the crack was near to achieve the critical length. It was also observed the Ds and Dt values presented an inverse behavior due the increase of the crack propagation velocity, while Ds raised the Dt values diminished related to the K evolution. Hence, the structural dimension is the responsible to describe the anisotropic behavior of the relief due the stress fields evolution in the crack tip... (Complete abstract click eletronic access below)

Made available in DSpace on 2014-06-11T19:27:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-07-08Bitstream added on 2014-06-13T20:55:51Z : No. of bitstreams: 1 campos_ka_me_guara.pdf: 6227902 bytes, checksum: ee44aa7120c6145b6c7adb73f08cf527 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Superfícies de fratura expressam a seqüência de eventos de liberação de energia com a propagação de trincas, mostrando a relação entre os componentes da estrutura, campos de tensões locais e a formação de texturas típicas em seu relevo. No caso dos compósitos de matriz polimérica, a evolução das formações topográficas pode indicar as linhas de ação de carga, os efeitos de degradação pelo ambiente ou os defeitos de processamento. Sendo assim, o objetivo deste trabalho é avaliar se as regiões de relevo formadas pelos diferentes mecanismos de propagação de trincas na fratura de compósitos termorrígidos, carbono/epóxi, podem ser relacionadas a diferentes valores de dimensão fractal, correspondendo à sua influência sobre a tenacidade. Os corpos-de-prova de compósito carbono/epóxi foram divididos em três grupos, sendo natural, com condicionamento higrotérmico e com condicionamento ultravioleta. As fraturas analisadas foram provenientes de ensaios DCB, em modo I de carregamento, sendo a aquisição das imagens feitas com o uso de microscópio óptico de reflexão e as topografias das superfícies obtidas pelo método de reconstrução por extensão de foco, calculando-se os valores de dimensão fractal com o uso dos mapas de elevações. A dimensão fractal foi classificada como: dimensão monofractal (Df), quando a fratura é descrita por um único valor; ou dimensão textural (Dt), que é uma análise macroscópica da fratura, combinada com a dimensão estrutural (Ds), que é uma análise microscópica. Os resultados demonstraram que não há relação entre Df e GIC, como proposto por Mecholsky, em seus trabalhos, não sendo esta medida uma propriedade do material. Quanto a Dt, esta medida não pode descrever qualquer propriedade do material, pois se restringe à descrição local do processo de fratura. Já Ds, descreve... / Fracture surfaces express the sequence of events of energy release with crack propagation, showing the relationship between the components of the structure, local stress fields and the formation of textures in his typical relief. In the case of polymer matrix composites, the evolution of topographic features may indicate the lines of action of load, the effects of degradation of the environment or processing defects. Therefore, the objective this work is to assess if the relief regions formed by different mechanisms of crack propagation in the fracture of thermosetting composites, carbon / epoxy, may be related to different values of fractal dimension, corresponding to its influence on toughness. Composite carbon / epoxy specimens were divided into three groups, namely natural, with hygrothermal conditioning and ultraviolet conditioning. The fractures were analyzed from DCB tests in mode I loading, with the acquisition of images by using an optical microscope and the surface topographies obtained by an extended depth-of-field method, calculating the values of fractal dimension with the use of elevation maps. The fractal dimension was classified as: monofractal dimension (Df), when the fracture is described by a single value, or texture dimension (Dt), which is a macroscopic fracture, combined with the structural dimension (Ds), which is a microscopic analysis. The results showed that there isn´t relationship between Df and GIC, as proposed by Mecholsky in his work, since this measure is not a material property. As for Dt, this measure cannot describe any property of the material, because it restricts the description of the process to local fracture conditions. In other way, Ds describes the micro-relief and is associated to the forces involved in the rupture of atomic bonds and, thus, to the association between micromechanics and microstructure... (Complete abstract click electronic access below)

Orientador: Luis Rogério de Oliveira Hein / Banca: Ana Paulo Rosifini Alves Claro / Banca: Durval Rodrgigues Júnior / Resumo: Superfícies de fratura apresentam a evolução entrópica durante a propagação de trincas, demonstrando relações entre componentes estruturais, campos de tensões locais e formações típicas de relevo. No caso das ligas metálicas, a evolução das formações topográficas pode indicar as linhas de ação de carga, a dinâmica do processo de fratura, falhas de uso ou de processamento, e outros. Neste trabalho, foram realizadas análises da relação entre a dimensão fractal e a variação do fator intensidade de tensão, da relação entre a dimensão fractal e a posição à frente da trinca, além do estudo da influência da espessura nos valores de dimensão fractal. Esses estudos foram efetuados a partir da topografia das superfícies fraturadas do aço 15-5PH obtidas em ensaios de propagação de trincas por fadiga, conforme ASTM E647. A investigação das fraturas foi feita por meio do método de reconstrução por extensão de foco, com o qual foi possível calcular os valores de dimensão monofractal (Df), dimensão textural (Dt) e dimensão estrutural (Ds), utilizando os mapas de elevações gerados pelo método. Os resultados das análises mostraram que os valores de Ds foram sensíveis à mudança dos micromecanismos de fratura, sendo que eles aumentaram até a transição do estágio II para o estágio III, sofrendo uma leve queda quando a trinca se propagava de forma instável e, em seguida, voltaram a aumentar quando a trinca estava perto de atingir seu tamanho crítico. Também foi observado que os valores de Ds e Dt se comportaram de forma inversa com o aumento da velocidade de propagação da trinca, em que os valores de Ds aumentaram e os de Dt decresceram em relação à evolução de K. Sendo, então, a dimensão estrutural responsável por descrever o comportamento anisotrópico do relevo, devido à evolução... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Fracture surfaces present the entropic evolution during the crack propagation, demonstrating relationship between structural components, local stress fields and typical relief formation. Regarding metallic alloys, the evolution of topographical formations may indicate the load action lines, the dynamism of the fracture process, during the processing or in use failures. In this work, it was performed the analysis of the relation between the fractal dimension and the stress intensity factor deviation, the relation between the fractal dimension and the crack tip position and also the study of the thickness influence in the fractal dimension values. These studies were performed by means of the topography of the 15-5PH steel fracture surfaces obtained throughout the fatigue crack propagation tests, in accordance with ASTM E647. The fractures investigation was executed using the 3-D reconstruction by extended depth of field method, allowing the possibility to calculate the values of the monofractal dimension (Df), textural dimension (Dt) and structural dimension (Ds), using of the elevation maps generated by the method. The analysis results showed that Ds was sensitive to changes on fracture micromechanisms, once they have increased up to the stage II to stage III transition, appearing a smooth reduction during the crack propagation at the unstable region and, after this, the values turned back to increase when the crack was near to achieve the critical length. It was also observed the Ds and Dt values presented an inverse behavior due the increase of the crack propagation velocity, while Ds raised the Dt values diminished related to the K evolution. Hence, the structural dimension is the responsible to describe the anisotropic behavior of the relief due the stress fields evolution in the crack tip... (Complete abstract click eletronic access below) / Mestre

Yttria stabilized zirconia (YSZ) is a polymorph with possible phase transformation toughening occurring during impact. The fractography and mechanical properties of laminated alumina and YSZ were studied in this thesis. Five sample types were studied in this thesis: (5:5) Al2O3/YSZ (a sequence of 5 alumina tapes stacked on 5 YSZ tapes), (5:5) Al2O3/YSZ (1 wt.% Pure ZrO2), (7:3) Al2O3/YSZ, Al2O3, and YSZ. Scanning electron microscopy (SEM) and X-ray microscopy (XRM) were used to study morphology and crack propagation with three-point tests performed to study the flexural strength. X-ray diffraction (XRD) spectra of all samples pre and post three-point tests were examined to determine if a change in monoclinic zirconia occurred. The combination of SEM and XRM data found microcracks in the YSZ layers of Al2O3/YSZ laminates with none present on YSZ laminates, leading to the conclusion tensile stress was performed on YSZ during sintering with Al2O3. Fracture patterns show a curving of cracks in Al2O3 layers and abrupt, jagged breaks in YSZ layers with crack forking at major YSZ microcrack regions. YSZ laminates were found to have the highest average flexural strength, but a very high standard deviation and low sample count and Al2O3 laminates having the second highest flexural strength. The (7:3) Al2O3/YSZ laminates had a significant increase in flexural strength compared to both types of (5:5) Al2O3/YSZ laminates. Significant change in monoclinic presence was not found except for the (5:5) Al2O3/YSZ (1 wt.% Pure ZrO2) laminates.

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