Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-08-10T11:35:30Z No. of bitstreams: 1 AnaClaudiaDeMeloCaldasBatista_TESE.pdf: 6455968 bytes, checksum: e236bd6847574ecdc738c08d4eb6a4fb (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-08-10T16:05:11Z (GMT) No. of bitstreams: 1 AnaClaudiaDeMeloCaldasBatista_TESE.pdf: 6455968 bytes, checksum: e236bd6847574ecdc738c08d4eb6a4fb (MD5) / Made available in DSpace on 2017-08-10T16:05:11Z (GMT). No. of bitstreams: 1 AnaClaudiaDeMeloCaldasBatista_TESE.pdf: 6455968 bytes, checksum: e236bd6847574ecdc738c08d4eb6a4fb (MD5) Previous issue date: 2017-06-12 / Os tecidos h?bridos a base de fibras sint?ticas v?m sendo desenvolvidos pelo setor industrial como nova alternativa de refor?o para comp?sitos polim?ricos. Neste sentido, surge a necessidade do conhecimento das caracter?sticas mec?nicas desses comp?sitos polim?ricos com tecidos h?bridos, que at? o presente momento foram pouco estudados. Em determinadas condi??es de projetos, tr?s caracter?sticas s?o significativas: anisotropia, presen?a de descontinuidades geom?tricas e forma de hibridiza??o. Esta tese busca contemplar todas essas influ?ncias com o estudo de dois laminados comp?sitos, utilizando dois tecidos: o tecido h?brido de fibras de Carbono/Vidro e o tecido h?brido de fibras de Carbono/Aramida, ambos tendo como matriz a resina ep?xi ?ster Vin?lica. Para obten??o dos laminados foi utilizado o processo de fabrica??o de lamina??o manual (Hand-lay-up). Para o estudo proposto foram realizados os ensaios de tra??o uniaxial nos corpos de provas de forma que todos os diferentes tipos de fibras tivessem sua orienta??o coincidente com a dire??o da carga aplicada, al?m da orienta??o das fibras a ?45? com o objetivo de conhecer o comportamento ao cisalhamento para ambos os laminados. Os ensaios foram realizados, tanto para a condi??o original (sem furo) quanto para a condi??o com a descontinuidade geom?trica (caracterizada como um furo central, que para a orienta??o de fibra de melhor desempenho mec?nico teve seu di?metro vari?vel). Estudos das propriedades de resist?ncia ?ltima, rigidez e caracter?sticas da fratura mec?nica (macrosc?pica e microsc?pica) foram desenvolvidos. Para influ?ncia da rela??o w/D (largura do CP/di?metro do furo) foi realizado um estudo anal?tico tendo como base a avalia??o do fen?meno da concentra??o de tens?o a partir dos crit?rios de falhas: Crit?rio da Tens?o Pontual (Point Stress Criterion -PSC) e Crit?rio da Tens?o M?dia (Average Stress Criterion - ASC), assim como um estudo num?rico utilizando o M?todo de Elementos Finitos. Nesses estudos o objetivo central foi ? determina??o do fator de concentra??o de tens?o (K) dos materiais propostos, usando tanto a influ?ncia dos m?dulos el?sticos quanto unicamente dos par?metros geom?tricos. Os estudos mostraram que o comportamento mec?nico e caracter?stica da fratura foram fortemente influenciados pela anisotropia e hibridiza??o e a descontinuidade geom?trica. Os modelos anal?ticos e num?ricos obtiveram resultados em concord?ncia com os encontrados na literatura. Palavras chaves: Tecidos h?bridos, descontinuidade geom?trica, anisotropia, hibridiza??o. / Hybrid synthetic fiber-based fabrics have been developed by the industrial sector as a new reinforcement alternative for polymer composites. In this respect, there is a need to know the mechanical characteristics of these hybrid polymer composite fabrics, which have been little studied to date. Under project conditions, three characteristics are significant: anisotropy, geometric discontinuities and type of hybridization. This thesis aims to investigate all of these influences by studying two composite laminates, using two fabrics: a hybrid carbon/glass fiber fabric and a hybrid carbon/aramid fiber fabric, both with epoxy vinyl ester resin as matrix. The manufacturing process used was hand lay-up to obtain the laminates. Uniaxial tensile tests were conducted on test specimens so that all the different types of fibers were oriented in the direction of the applied load, in addition to fiber orientation at ?45? in order to determine the shear behavior of the laminates. The tests were carried out in both the original condition (without hole) and with geometric discontinuity (characterized as a central hole, whose diameter was variable for orientation of high mechanic performance fiber). A number of studies on ultimate strength and fracture mechanics characteristics (macroscopic and microscopic) have been conducted. To determine the influence of the w/D ratio (width of test specimen/diameter of the hole), an analytical study was performed based on stress concentration using Point Stress Criterion (PSC) and Average Stress Criterion (ASC) failure theories, as well as a numerical study using the Finite Elements Method. In these studies, the primary objective is to determine the stress concentration factor (K) of the proposed materials, using both the influence of elastic modulus and geometric parameters. The studies showed that mechanical behavior and fracture characteristics were strongly influenced by anisotropy, hybridization and geometric discontinuity. The analytical and numerical models obtained results showing good agreement with those reported in the literature.

Made available in DSpace on 2014-12-17T14:58:20Z (GMT). No. of bitstreams: 1 AnaCMCB_DISSERT.pdf: 5204946 bytes, checksum: 70bedde30acbc8578034105c8c4fc24e (MD5) Previous issue date: 2013-07-25 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The utilization of synthetic fibers for plastic reinforcement is more and more frequent and this growing interest requires that their mechanic behavior under the most variable conditions of structural applications be known. The use of such materials in the open and exposed to the elements is one of them. In this case, it becomes extremely necessary to study their mechanical properties (strength, stiffness) and the mechanism of fracture by which the environment aging them out. In order to do that, the material must be submitted to hot steam and ultraviolet radiation exposure cycles, according to periods of time determined by the norms. This study proposal deals with the investigation of accelerated environmental aging in two laminated polymeric composites reinforced by hybrid woven made up of synthetic fibers. The configurations of the laminated composites are defined as: one laminate reinforced with hybrid woven of glass fibers/E and Kevlar fibers/49 (LHVK) and the other laminate is reinforced with hybrid tissue of glass fibers/E and of carbon fibers AS4 (LHVC). The woven are plane and bidirectional. Both laminates are impregnated with a thermofix resin called Derakane 470-300 Epoxy Vinyl-Ester and they form a total of four layers. The laminates were industrially manufactured and were made through the process of hand-lay-up. Comparative analyses were carried out between their mechanical properties by submitting specimen to uniaxial loading tractions and three-point flexion. The specimen were tested both from their original state, that is, without being environmentally aging out, and after environmental aging. This last state was reached by using the environmental aging chamber / O interesse na utiliza??o dos pl?sticos refor?ados por fibras sint?ticas ? cada vez mais crescente e esse grande interesse na utiliza??o dos mesmos faz com que seja necess?rio o conhecimento do comportamento mec?nico desses materiais sob as mais variadas condi??es de aplica??o estrutural. Dentre estas pode ser destacada a aplica??o desses materiais em situa??es em o elemento encontra-se exposto ? intemp?rie, e nesse caso os estudos das propriedades mec?nicas (resist?ncia, rigidez) al?m do mecanismo fratura frente ao envelhecimento ambiental s?o de extrema necessidade. Para tanto, submeter o material ? per?odos c?clicos de exposi??o ao vapor aquecido e ? de radia??o ultravioleta, por tempo definido em norma, se faz necess?rio. A presente proposta de trabalho de investiga??o consiste no estudo do envelhecimento ambiental acelerado em dois laminados comp?sitos polim?ricos refor?ados por tecidos h?bridos ? base de fibras sint?ticas. As configura??es dos laminados comp?sitos s?o definidas como: um laminado refor?ado com tecido h?brido de fibras de vidro/E e de fibras kevlar/49 (LHVK) e outro laminado refor?ado com tecido h?brido de fibras de vidro/E e de fibras de carbono AS4 (LHVC). Os tecidos s?o dos tipos planos e bidirecionais. Ambos os laminados foram impregnados a base de resina termofixa Derakane 470-300 Ep?xi Vinil-Ester e constitu?dos com quatro camadas no total. Os laminados t?m fabrica??o industrial e foram obtidos atrav?s do processo de lamina??o manual (Hand-lay-up). Foram realizados estudos comparativos entre as propriedades mec?nicas sob a a??o dos carregamentos de tra??o uniaxial e flex?o em tr?s pontos, nas condi??es dos corpos de prova sem o efeito do envelhecimento ambiental (estado original) e sob o efeito desse envelhecimento (estado envelhecido). O envelhecimento ambiental foi acelerado atrav?s do uso da c?mara de envelhecimento