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Search Results: 1 - 10 of 606768 matches for " d'Almeida José Roberto M. "
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Ensaios de Pullout em fibras lignocelulósicas: uma metodologia de análise
Monteiro, Sergio N.;d'Almeida, José Roberto M.;
Matéria (Rio de Janeiro) , 2006, DOI: 10.1590/S1517-70762006000300004
Abstract: pullout testes are used to determine the fiber's critical length, lc , and the interface shear strength, t , associated with the stress transfer from the matrix to the fiber in a composite material. in this work, the methods of performing and interpreting pullout tests in lignocellulosic fibers were evaluated. results from pullout tests in piassava, coir and curauá natural fibers were compared to others published on synthetic fibers in terms of procedures to obtain lc and t. based on the marked differences that exist between the behavior of natural fibers with respect to that of synthetic fibers, a proper methodology is proposed to evaluate the results from pullout testing in lignocellulosic fibers.
Compara??o do comportamento à flex?o com restri??es à deflex?o de placas de compósitos de matriz polimérica epoxídica em fun??o do tipo de fibra de refor?o
Morais, Willy A. de;dAlmeida, José Roberto M.;
Polímeros , 2003, DOI: 10.1590/S0104-14282003000300008
Abstract: thin plates of epoxy resin matrix composites reinforced with glass, carbon and aramid fibers, as well as a plate from a hybrid glass-aramid composite, were submitted to flexure tests. the specimens were fixed in order to conduct the testes under restricted conditions of deflection. the experimental results of the maximum deflection agreed qualitatively with the ritz method of energy balance. carbon fiber reinforced composites showed the highest values for the initiation energy and for the maximum force. both results were attributed to the high intrinsic properties of carbon fibers. the specific properties of the hybrid composite were higher than the properties of the glass or aramid reinforced composites. this synergistic effect is indicative of a properly designed hybrid composite. the macroscopic failure mode of all composites was similar. at the front face the interaction between the composite and the indenter followed the behavior of hertz law. at the rear face, delamination occurred preferentially.
Efeito da presen?a de defeitos no comportamento mecanico de juntas coladas carbono-epoxi
Berry, Nara G.;d'Almeida, José Roberto M.;
Polímeros , 2000, DOI: 10.1590/S0104-14282000000300010
Abstract: nowadays, bonded joints are been widely used to replace mechanically joined parts. the influence of defects on the mechanical behavior of these joints must be determined if their reliability is to be ascertained. in this work, the mechanical behavior of single lap joints was evaluated as a function of the presence and size of defects on the bonded area. the results obtained indicate that the models developed for determining the strength of flawless single lap joints can be employed to model the behavior of single lap joints with defects.
Efeito da presen a de defeitos no comportamento mecanico de juntas coladas carbono-epoxi
Berry Nara G.,d'Almeida José Roberto M.
Polímeros , 2000,
Abstract: Juntas unidas por ades o vêm sendo largamente empregadas em substitui o a pe as unidas por métodos convencionais de fixa o mecanica. A confiabilidade destas juntas deve considerar o efeito da presen a de defeitos na área colada sobre o comportamento mecanico da pe a. Neste trabalho analisou-se o comportamento mecanico de juntas sobrepostas simples em fun o da presen a de defeitos. Foi verificado, também, a adequa o para as juntas com defeitos dos principais modelos teóricos desenvolvidos para juntas sem defeitos.
Compara o do comportamento à flex o com restri es à deflex o de placas de compósitos de matriz polimérica epoxídica em fun o do tipo de fibra de refor o
Morais Willy A. de,d?Almeida José Roberto M.
Polímeros , 2003,
Abstract: Placas finas de compósitos de matriz polimérica epoxídica refor ada por fibras de vidro, carbono ou aramida, bem como placas de um compósito híbrido vidro-aramida, foram submetidas a ensaios de flex o. As condi es de fixa o dos corpos de prova foram tais que o ensaios foram realizados com deflex o restrita. Os resultados experimentais obtidos para a deflex o máxima dos compósitos puderam ser qualitativamente previstos usando-se o método de balan o de energia de Ritz. Os compósitos refor ados por fibras de carbono apresentaram os maiores valores de energia de inicia o e de for a máxima, o que foi atribuído às altas propriedades intrínsecas das fibras. As propriedades específicas do compósito híbrido foram superiores às dos compósitos apenas com fibras de vidro ou fibras aramidas. Este efeito sinergístico indicou um projeto adequado na fabrica o deste compósito. O modo de falha macroscópico de todos os compósitos foi semelhante. Na face frontal, a intera o compósito - pun o seguiu o comportamento previsto pela Lei de Hertz. Na face posterior, houve preferencialmente delamina o.
Efeito da interface fibra/matriz sobre a resistência de compósitos poliméricos refor?ados com fibras de coco
Monteiro, Sergio N.;Terrones, Luiz Augusto H.;Carvalho, Eduardo A. de;d'Almeida, José Roberto M.;
Matéria (Rio de Janeiro) , 2006, DOI: 10.1590/S1517-70762006000400005
Abstract: the characteristics of the fiber/matrix interface in polyester composites reinforced with coir fibers have been evaluated. this was carried out both, by measuring the interfacial shear strength and by microstructural observation of the coir fibers/polyester resin contact area. tests of coir fiber extraction from resin sockets allowed an analysis by scanning electron microscopy of regions where the fibers underwent rupture or suffered pullout during extraction. the results showed interfacial shear strength similar to other lignocellulosic fibers. moreover, a reasonable interface adhesion was obtained owing to the heterogeneous nature of the coir fibers, which facilitates the resin impregnation.
Avalia??o do efeito de um óleo parafínico sobre o comportamento físico-químico de tubula??es de polietileno de alta densidade
Torres, Amélia A. U.;d'Almeida, José Roberto M.;Habas, Jean-Pierre;
Polímeros , 2010, DOI: 10.1590/S0104-14282011005000001
Abstract: the effects caused by a paraphinic oil on the physicochemical behavior of high-density polyehtylene pipes were investigated, as a function of time and temperature. these effects were evaluated by thermogravimetric and gravimetric analysis and by ftir. the gravimetric data were satisfactorily described using the fick's law, and the ftir results showed that no main structural modifications have occurred after exposure of the hdpe pipes to this oil. from the results obtained it was concluded that physical aging was occurring, since the chemical structure of the polymer was not altered.
Efeito de impactos repetidos de baixa energia em compósitos pultrudados
Morais, Willy Ank de;D'Almeida, José Roberto M.;Godefroid, Leonardo B.;
Polímeros , 2001, DOI: 10.1590/S0104-14282001000100008
Abstract: damage can be produced in polymers composite materials submitted to low energy impact events. the cumulative effect of such repetitive impacts could finally cause failure of the structure. in this work two pultruded composites were submitted to drop-weight tests. the results obtained were evaluated according to the fiber distribution in the composites. it was also shown that the presence of a resin rich layer in one of the composites strongly reduces the performance of this composite. this behavior was associated with the development of cracks in the resin rich layer. the number of repeated impacts, the duration of the impact and the shape of the damaged area were correlated to the presence, or the absence, of the resin rich layer. the results obtained also show that the difference between the microstructures of the pultruded profiles analyzed is more significant when low energy impact tests were performed (drop height : 0.5 m). for the tests performed with a higher impact energy (drop height : 1 m) the microstructure plays only a secondary role.
Efeito de impactos repetidos de baixa energia em compósitos pultrudados
Morais Willy Ank de,D'Almeida José Roberto M.,Godefroid Leonardo B.
Polímeros , 2001,
Abstract: Danos internos podem ser gerados em compósitos de matriz polimérica submetidos a impactos de baixa energia. O efeito repetido de eventos desse tipo pode levar, eventualmente, à falha da estrutura. Neste trabalho dois tipos de perfis pultrudados foram submetidos a impactos por queda livre de peso de 0,5 m e 1,0 m de altura. Os resultados obtidos foram analisados em fun o da disposi o das fibras nos perfis e mostram que a existência de uma camada rica em resina em um dos perfis, contribui para reduzir significativamente o desempenho deste perfil. Este comportamento foi associado à forma o prematura de trincas na camada rica em resina. O número de eventos de impacto, o tempo de dura o de cada choque e a forma da área danificada foram correlacionados com a presen a, ou n o, da regi o rica em resina. Os resultados obtidos indicam ainda que a diferen a na microestrutura dos perfis analisados é mais significativa para os ensaios de menor energia (queda de 0,5 m). Para os ensaios de maior energia (queda de 1 m) a configura o do material teve apenas uma importancia secundária.
Tenacidade ao entalhe por impacto Charpy de compósitos de poliéster refor?ados com fibras de pia?ava
Monteiro, Sergio N.;Aquino, Regina Coeli M. P.;Lopes, Felipe P. D.;d'Almeida, José Roberto M.;
Matéria (Rio de Janeiro) , 2006, DOI: 10.1590/S1517-70762006000300006
Abstract: rigid piassava fibers of the specie attalea funifera mart have been recently investigated as effective reinforcements for polymeric composites. the works performed so far in these composites have shown a reasonable increase in the mechanical strength with the amount of fiber. since some possible application for piassava composites would demand resistance to impact, the objective of the present work was to carry out a study on the notch toughness, measured by a pendulum hammer, of rigid and aligned piassava fiber reinforced polyester matrix composites. standard specimens of composites with up to 40 wt.% of continuous piassava fibers were evaluated by means of charpy tests and their fracture microstructure investigated by scanning electron microscopy. the results obtain showed that piassava composites present a notch toughness behavior that is comparatively superior to that of other natural fiber reinforced polymeric composites.
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