Para confeccionar próteses faciais e reabilitar aqueles pacientes com perdas anatômicas, são empregados diversos materiais, destacando-se entre estes os flexíveis,devido á semelhança estética que apresentam com a pele humana. O padrão de qualidade dos materiais é liderado por produtos estrangeiros, tornando difícil a obtenção e, por tanto, a aplicação dos mesmos em território nacional. Devido à necessidade de se ter materiais nacionais com qualidade semelhante aos importados, este trabalho mensurou dois materiais, a resina resiliente CLASSIFLEX e o silicone médico ORTHO PAUER, ambos de produção nacional, seguindo as normas da ASTM (American Standard for testing materiais). Foram testadas dureza Shore A, resistência ao rasgamento, resistência a tração e alongamento de ruptura. Os valores obtidos foram analisados estatisticamente e comparados entre sim. Os valores de resistência a tração, resistência ao rasgamento e dureza Shore A, dos materiais testados foram baixos quando comparados com os valores encontrados em outras pesquisas .Os valores de Alongamento de ruptura se encontram dentro dos valores aceitáveis para matérias de uso em reabilitação buco maxilo facial. / To fabricate and create facial prosthesis for those patients with anatomical loss, maxillo facial protesiologist use differet materials. Flexible materials has being used mostly because of their aesthetic similarity with the skin. The standard for quality in prostethic materilas is led by foreign products, making it difficult to obtain and apply these materials in national territory. Due to the necessity of giving new and better materilas the CLASSIFLEX resilient resin and the ORTHO PAUER medical silicone, both of domestic production, were selected to test the fisical properties of: Shore A hardness, elongation, tensile strength and tear strenght. The specimens were made following the parameters indicated by the ASTM and each test was performed. The values obtained were analyzed statistically and compared. The results obtained may conclude that the physical properties of tensile srtrenght, tear strenght and Shore A hardness were low when compared with the results observed in other similar studies. The values obtained from the elongation test shows similarity of other values obtained by past studies.

Avaliou-se a taxa de degradação de elásticos ortodônticos de látex de diferentes fabricantes e diâmetros em diversos intervalos de tempo. Grupos de 15 elásticos de força média dos fabricantes AmericanOrthodontics (Sheboygan, Wis, EUA), Tp (La Porte, IN, EUA), Morelli (Sorocaba, SP, Brasil) e Uniden (Sorocaba, SP, Brasil); de diâmetros 3/16, 1/4 e 5/16 foram analisados nos intervalos de 0,1,3,6,12 e 24 horas, totalizando-se 1080 espécimes. Os elásticos foram estirados individualmente à distância de 30mm, respeitando-se o intervalo de um minuto entre cada estiramento. Os materiais foram acondicionados imersos em água deionizada à 37C. Realizou-se leitura das forças na máquina de ensaios Emic DL 500 (Emic Co, Sao Paulo, Brasil) à velocidade de 30 mm/min, com uma célula de 2Kg (Emic Co, Sao Paulo, Brasil). A leitura de cada elástico consumiu aproximadamente um minuto. Teste Kruskal-wallis com correções por Dunns aferiu significância estatística dos resultados. Foram observadas diferenças entre os grupos analisados, exceto às marcas Morelli e Tp. Foram significativas as inferências das variáveis tempo e marca comercial. Em 0 hora, a relação entre as forças geradas foi Morelli>AO>Uniden>Tp para elásticos 3/16 (p=0,0016) e 1/4 (p=0,0016) e, de Morelli>AO>Tp>Uniden para elásticos 5/16 (p=0,0087). Após 24 horas, as porcentagens de degradação dos elásticos foram AO>Morelli>Uniden>Tp no diâmetro 3/16; AO>Tp>Morelli>Uniden no diâmetro 1/4 e Tp>AO>Uniden>Morelli para elásticos de diâmetro 5/16. O comportamento no intervalo de 0-24 horas demonstrou uma queda acentuada no período de 0-3 horas, um ligeiro aumento em 3-6 horas, seguido de uma queda progressiva no intervalo de 6-24 horas. / The purpose of this study was to evaluate the force relaxation of different brands and diameters of latex elastics occurring during different times. Groups of 15 medium forces elastics from manufacturers: American Orthodontics (Sheboygan, Wis, USA), Tp (La Porte, IN, USA), Morelli Orthodontics (Sorocaba, SP, Brazil) and Uniden Orthodontics (Sorocaba, SP, Brazil) with diameters: 3/16, 1/4 and 5/16 inch size were tested at 0,1,3,6,12,24 hours, making a total of 1080 specimens. An apparatus was designed to simulate oral environments during elastics stretching. The forces were read after 1,3,6,12 and 24-hour periods in Emic testing machine (Emic Co, Sao Paulo, Brazil) with 30 mm/min cross-head speed and load cell of 2Kg Emic force (Emic Co, Sao Paulo, Brazil). Kruskal-Wallis and Dunns tests were used to identify statistical significance. Overall, there were statistically differences among the different manufacturers at all observation intervals, except between Morelli and Tp. Significantly variability were seen in Morelli and Uniden force delivery. The relationships among loads at 0-hour time period were as follows: Morelli>AO>Uniden>Tp for 3/16 (p=.0016) and 1/4 elastics (p=.0016) and Morelli>AO>Tp>Uniden for 5/16 elastics (p=.0087). The forces relaxation over the 24-hour time period were AO>Morelli>Uniden>Tp for 3/16 elastics; AO>Tp>Morelli>Uniden for 1/4; and Tp>AO>Uniden>Morelli for 5/16 elastics.The force decay pattern show a notable drop-off of forces during 0-3 hours, a slight increase in force values from 3-6 hours and a progressive force decay was seen over 6-24 hours.

A reciclagem de diversos tipos de materiais tem adquirido importância nos últimos anos. Problemas ambientais graves como o acúmulo de rejeitos e a poluição atmosférica, causados pelo crescente consumo de materiais poliméricos, incentivam estudos para o desenvolvimento de diferentes formas de reaproveitamento. Entretanto, a reciclagem de polímeros elastômeros tem demonstrado grande complexidade, pois o material depois de vulcanizado não pode ser remoldado pelo simples aquecimento. A desvulcanização por microondas é uma técnica promissora para contornar este problema, uma vez que possibilita restituir a capacidade de moldagem dos elastômeros. Neste trabalho foi feito um estudo sobre a desvulcanização por micro-ondas em processo contínuo e em batelada do elastômero estireno-butadieno (SBR) com diferentes quantidades de negro de fumo e em diferentes condições de processamento, de modo a avaliar os processos de desvulcanização e esclarecer melhor os fenômenos e reações químicas envolvidas. A eficiência dos diferentes sistemas de desvulcanização adotados foi avaliada por meio de análises termogravimétricas (TG), dinâmico-mecânicas (DMA), calorimetria exploratória diferencial (DSC), espectroscopia no infravermelho (FTIR), espectrometria de ressonância magnética nuclear (RMN), densidade de ligação cruzada e teor de gel. A desvulcanização foi mais efetiva no elastômero SBR com maiores teores de negro de fumo, empregando o sistema de desvulcanização em batelada com uma única fonte de radiação, enquanto que a desvulcanização contínua não apresentou resultados relevantes para o sistema adotado. O material desvulcanizado demonstrou mudanças químicas e físicas consideráveis na sua estrutura. Assim, a reciclagem de elastômeros utilizando a energia das micro-ondas torna-se possível e provoca mudanças estruturais no material para borracha com altos teores de negro de fumo utilizando o sistema batelada. / The recycling of several materials has acquired importance in the last few years. Serious environmental problems as the increase in waste material and air pollution, caused by the growing consumption of polymeric material, stimulate works to development of distinct ways of reclamations. However, the recycling of elastomers has demonstrated more complexity than other polymeric materials because, after vulcanized, the material can not be remolded by simple heating. The microwave devulcanization is a promissory technique to solve this problem, in as it makes it possible to replace the remold capacity of elastomers. In this work it was studied the devulcanization by microwave in continuous and batch processes of styrene-butadiene rubber (SBR) with different amount of carbon black (CB) and in different process conditions, to evaluate the devulcanization process and to clarify the involved phenomena and chemical. The efficiency of distinct devulcanization systems was evaluated through thermogravimetric analyses (TG), dynamic-mechanical analysis (DMA), differential scattering calorimetric (DSC), Fourier transformed infrared (FTIR), nuclear magnetic resonance (NMR), crosslink density and gel content analysis. The devulcanization was more effective in SBR elastomer with higher amount of carbon black, used the batch systems devulcanization with a single source of radiation, whereas the continuous devulcanization did not show relevant results to the adopted system. The devulcanized material exhibited considerable chemical and physical alteration in its structure. Thus, the elastomers recycling using the microwave energy is possible and generates structural modification in the material for rubber with high amount of carbon black in batch system.

Durant ce travail, nous avons étudié les propriétés mécaniques et de fracture d'élastomères à réseaux multiples synthétisés par des étapes successives de gonflement/polymérisation inspirées de l'architecture moléculaire développée par Gong pour les doubles réseaux hydrogels. Une méthode de synthèse plus versatile a été utilisée pour varier de façon continue le pré-étirement isotrope du premier réseau λ0, qui contrôle le module d'Young et le durcissement. Dans le cas d'une dilution importante du premier réseau (<10%), une scission moléculaire apparaît à grande déformation dans le réseau pré-étiré sans rompre le matériau. Le taux de dilution contrôle la quantité d’endommagement et donc la pente de la courbe contrainte-déformation. Finalement, pour les systèmes les plus dilués (<3%), une striction est observée au-dessus d’un seuil de contrainte. Changer le taux de réticulant du premier réseau ou les monomères utilisés ont conduit par ailleurs à l’obtention de comportements mécaniques similaires. L’énergie de fracture Γ est une fonction croissante de λ0. Des techniques de visualisation locale comme la Corrélation d’Image Numérique et l’intégration de molécules méchanoluminescentes ont été utilisées pour décrire une zone d’endommagement en tête de fissure dont la taille augmente avec λ0. Enfin, le mécanisme de renforcement des élastomères à réseaux multiples a pu être partiellement décrit dans le contexte du modèle de Brown sur les doubles réseaux. / We investigated systematically the mechanical and fracture properties of multiple network elastomers synthesized by successive swelling/polymerization steps inspired by the molecular architecture of Gong’s double network gels. A more versatile synthesis method was used to vary continuously the isotropic degree of prestretching λ0 of the first network resulting in a wider range of mechanical behaviours, where λ0 controls the Young’s modulus at small strain and the strain hardening at large strain. If the first network is diluted enough (<10%) molecular bond breakage occurs in this prestretched network at high strain while avoiding sample failure. The degree of dilution controls the amount of damage and therefore the slope of the stress-strain curve. Finally, for the most diluted systems (<3%), a yield stress and a necking phenomenon was observed. Changing the degree of crosslinking of the first network or the monomers used led to the same qualitative mechanical behaviour. The fracture energy Γ was shown to be an increasing function of λ0 however different regimes could be distinguished with macroscopic fracture occurring before or after bulk damage was detected. Visualisation techniques such as Digital Image Correlation and embedded mechanoluminescent molecules were used to map a damage zone in front of the crack tip, the size of which increased with λ0. Finally, the toughening mechanism of the multiple network elastomers could be understood in a nearly quantitative way within the framework of Brown's model of fracture of double network gels.

Objetivo: Comparar in vitro la degradación de fuerzas de tensión de los elásticos intermaxilares de látex y no látex DentsplyTM GAC de 5/16" (8mm) y 6oz (170g) expuestos y no expuestos a alimentos de consumo diario sometidos a dos tiempos de evaluación. Materiales y métodos: El estudio fue experimental in vitro. Se utilizó 136 elásticos intermaxilares de látex y no látex DentsplyTM GAC 5/16" (8mm) y 6oz (170g). Se dividieron en 4 grupos de 34 elásticos (Grupo A: Látex-agua destilada, Grupo B: No látex-agua destilada, Grupo C: Látex-comida diaria, Grupo D: No látex-comida diaria). Los gupos A y B fueron sumergidos en agua destilada a 37ºC, mientras que los grupos C y D fueron sumergidos a una dieta que se realizó en cuatro momentos (0, 3, 6 y 12 horas). A todos los grupos se le evaluó la fuerza de tensión a las 0 y 24 horas con la máquina Instron®(1mm/s). Los valores fueron registrados en Newtons (N). Resultados: Se encontraron diferencias estadísticamente significativas (p= 0,000) en el porcentaje de degradación de los elásticos intermaxilares de látex y de no látex DentsplyTM GAC. En valores porcentuales la degradación de los elásticos de látex fue 28.65% y los elásticos de no látex 38.47%. Sin embargo, al evaluar la degradación de los elásticos según la exposición a alimentos no se encontró diferencia estadísticamente significativa (p0.05). Conclusiones: En este estudio, se encontró mayor degradación de los elásticos de no látex. Por otro lado, a pesar de que los elásticos DentsplyTM GAC se expusieron a una dieta diaria, no existió mayor degradación. / Objective: To compare in vitro the degradation of tensile forces of latex intermaxillary elastics and non-latex DentsplyTM GAC 5/16 "(8mm) and 6 oz (170g) exposed and not exposed to daily consumption food subjected to two times of evaluation. Materials and methods: The study was experimental in vitro. It was used 136 intermaxillary elastics of latex and not latex DentsplyTM GAC of 5/16 "(8mm) and 6oz (170g). They were divided into 4 groups of 34 elastics (Group A: Latex – distilled water, Group B: Non-latex - distilled water, Group C: Latex - daily food, Group D: Non-latex - daily food). Groups A and B were submerged in distilled water at 37ºC, while groups C and D were submerged in a diet that was performed in four moments (0, 3, 6 and 12 hours). All the groups were evaluated the tensile strength at 0 and 24 hours with the Instron® machine (1mm/s). The values were recorded in Newtons (N). Results: Statistically significant differences (p = 0.000) were found in the percentage of degradation of the intermaxillary elastics of latex and non-latex DentsplyTM GAC. In percentage values the degradation of the elastics of latex was 28.65% and the elastics of non-latex 38.47%. However, when evaluating the degradation of the elastics according to food exposure, no statistically significant difference was found (p0.05) Conclusions: In this study, greater force degradation of non-latex elastics was found. On the other hand, although the Dentsply ™ GAC elastics were exposed to a daily diet, there was no further degradation. / Tesis

Thesis (M.S.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Science, Materials Science and Engineering Program, 2006. / Includes bibliographical references.

No description available.

The aircraft engine industry is constantly striving to increase the operating temperature and stresses in hot section engine components, a goal that can only be achieved by accurately modeling and predicting damage mechanisms of potential engine materials. The objective of this work is to develop physically-based models that are able to accurately predict the high temperature crack initiation behavior of Rene 88DT, a commonly used aircraft engine disk material, under low cycle fatigue (LCF) conditions. Two different microstructural conditions were produced by subjecting the material to two separate heat treatments; the heat treatments were selected so that grain size remains the same but the size distribution of the strengthening gamma prime precipitate is different between the two conditions. LCF experiments were performed on specimens from each condition at 650C and R = -1 under strain ranges of 0.66%, 0.75%, and 1.5%. A third microstructural condition with a similar grain size but different gamma prime size distribution was tested by another source at 650C and R = 0 under strain ranges of 0.66%, 0.79%, 0.94%, and 1.14%. The results indicate that there are two competing crack initiation mechanisms: initiation from a microstructural defect such as an inclusion and initiation from slip band cracking. A physically based model, in the form of a modified Fatemie-Socie parameter, is utilized to predict the crack initiation mechanism and approximate cycles to failure based on the microstructure of the material and applied strain. Long crack growth models are also developed to model crack growth from subsurface inclusions and surface semi-elliptical cracks. These models predict that long crack growth is a small portion of the total fatigue life in these conditions, which suggests that the majority of the fatigue life is spent initiating a dominant fatigue crack.

Segmented polyurethaneureas (SPUU) are thermoplastic elastomers with excellent elastic properties, high abrasion resistance and tear strength, making them very useful in numerous industrial applications ranging from microelectronics (slurry pad) to biomedical (artificial heart vessels) applications. The elastic and mechanical properties of these materials are strongly influenced by their two phase morphology. The factors that influence phase separation include difference in polarity between the hard and soft phases, composition and temperature. In general good phase separation results in materials with superior mechanical and elastic properties. Due to the immense potential applications of SPUU elastomers, there is a need for materials with higher strength. However, higher strength is not desired at the detriment of elasticity. If fact, stronger materials with enhanced elasticity are desired. In this thesis, high-strength SPUU elastomers were synthesized by incorporating reactive Laponite particles with surface-active free amine. The synthesis of pure SPUU is very complex, and addition of a reactive silicate further increases the complexity. To remedy this challenge, combinatorial methods and high-throughput screening techniques were used to optimize the diamine concentration and cure temperature. It was determined that pure SPUU elastomers prepared at a diamine stoichiometry of 85 100 mole %, and cured at 90 95 oC produced materials with higher strength and elongation at break. SPUU nanocomposites were prepared by maintaining the overall diamine stoichiometry at 95 mole %, and cured at 90 oC. Uniaxial tensile strength was optimized at a particle weight fraction of 1 wt. %, with a nearly 200 % increase in tensile strength and a 40 % increase in elongation at break, compared to pristine SPUU.

The structural response of unreinforced masonry elements strengthened with hybrid elastomeric/fiber materials was investigated through material characterization and flexural experiments. Material characterization tests were performed on various unreinforced and reinforced elastomeric materials to identify those materials that were best suited for use as structural retrofits. After material characterization was completed, the three most promising material systems were selected for further investigation, including one unreinforced elastomer film and two reinforced elastomer films with fiber orientations at 0/90° and +/- 45° relative to the major axis of the masonry elements. A series of four-point bending tests were performed on the selected masonry and epoxy bonded elastomer/fiber hybrid retrofits to determine the structural response of the composite systems. The experimental load-deformation response was used, along with material characterization results, in the development of a semi-empirical model to predict the static moment capacity of the strengthened masonry system. This model will be used in the development of reliable design criteria for masonry walls strengthened with these advanced materials.