Electromagnetic Properties of Multifunctional Composites Based on Glass Fiber Prepreg and Ni/Carbon Fiber Veil

Multifunctional composites combine structural and other physicochemical properties, with major applications in aeronautical, space, telecommunication, automotive, and medical areas. This research evaluates electromagnetic properties of multifunctional composites based on glass fiber woven fabric pre-impregnated with epoxy resin laminated together carbon fiber non-woven veil metalized with Ni. In this way, searching for possible application as radar absorbing structures or electromagnetic interference shielding structures. The scattering parameters, in the frequency range of 8.2 to 12.4 GHz, show that the epoxy resin/glass fiber prepreg allows the transmission of the electromagnetic waves through its microstructure, independently of the glass fiber reinforcement orientation (98% transmission, S-24 = -0.09 dB). However, the carbon fiber/Ni veil shows highly reflector behavior (91% reflection, S-22 = -0.43 dB). Energy dispersive spectroscopy of the veil, before and after nitric acid attacks, confirmed the Ni coating removal from the carbon fiber surface. Still, the scattering parameters show reflector behavior (77% reflection, S-22 = -1.13 dB), attributed to the electrical conductivity of carbon fibers. Multifunctional composites based on glass fiber/epoxy/carbon fiber/Ni veil laminates were processed by hot compression molding. The scattering parameters show that the laminates do not behave as good radar absorbing structures. Nevertheless, the laminates present promising results for application as light weight and low thickness structural composites with electromagnetic interference shielding effectiveness (91.4% reflection for 0.36 mm thickness and 100% for similar to 1.1 mm) for buildings, aircraft, and space components.Univ Estadual Paulista, Fac Engn Guaratingueta, Dept Mat & Tecnol, Ave Dr Ariberto Pereira Cunha,333 Portal das Coli, BR-12516410 Guaratingueta, SP, BrazilInst Technol Aeronaut, Dept Ciencia & Tecnol Aeroespacial, Lab Guerra Elect, Sao Jose Dos Campos, SP, BrazilUniv Fed Sao Paulo, Inst Ciencia & Tecnol Curso Engn Mat, Sao Jose Dos Campos, SP, BrazilUniv Fed Sao Paulo, Inst Ciencia & Tecnol Curso Engn Mat, Sao Jose Dos Campos, SP, BrazilWeb of Scienc

Synthesis and characterization of polyarylacetylene for use in the monolithic vitreous carbon processing

In this work, polyarylacetylene (PAA) prepolymer obtained from 1,4-diethynylbenzene was evaluated as polymeric precursor of monolithic vitreous carbon (MVC). The monomer 1,4-diethynylbenzene was synthesized and the PAA prepolymer was prepared with 13, 16 and 19 wt % of nickel catalyst. The best percentage of nickel catalyst considered was 13 wt %, due to the lower molecular weight and polydispersity index and higher carbon yield. The traditional production of MVC is obtained from phenolic and poly(furfuryl alcohol) resins, which require many hours to pyrolyze due to the large quantity of gases generated. Furthermore, the porosity is hard to control using these conventional resins. Polyarylacetylene releases little volatiles due to the polyaddition reaction and the aromatic rings in PAA chain also provide a high thermal stability, therefore the heat treatment could be faster without cracking the carbon material. This would also lower the cost of fabrication of MVC, in addition to the low porosity observed, making this polymer a good matrix for MVC.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Universidade Estadual Paulista Faculdade de Engenharia de GuaratinguetáUniversity of Washington Department of Materials Science and EngineeringUniversidade Federal de São Paulo (UNIFESP) Instituto de Ciência e TecnologiaUNIFESP, Instituto de Ciência e TecnologiaSciEL

Estudo das propriedades morfológicas, térmicas e mecânicas do compósito particulado de alumínio e polietileno de baixa densidade reciclados

Frente à crescente necessidade de recuperar o meio ambiente e seus recursos naturais, atualmente a recicla-gem e reutilização dos materiais torna-se uma das soluções sustentáveis mais visadas. Neste cenário, o pro-cessamento de compósitos particulados de alumínio em matriz termoplástica de polietileno de baixa densida-de (PEBD), provenientes da reciclagem de embalagens longa vida, apresenta-se de maneira atrativa para a obtenção de matéria prima para a construção civil, na fabricação de telhas de baixo peso, associado a baixo custo e elevada disponibilidade, dentre outras aplicações. Este trabalho tem por objetivo estudar as proprie-dades e o comportamento do compósito de polietileno de baixa densidade/alumínio reciclados. Com este ob-jetivo, foi realizada a avaliação morfológica do compósito a partir de microscopia óptica (MO), microscopia eletrônica de varredura (MEV) e espectroscopia por energia dispersiva de raios X (EDS), bem como avalia-dos os comportamentos térmico e mecânico deste material após estes terem sido submetidos à climatização higrotérmica e por radiação ultravioleta (UV). Para a avaliação térmica foram empregadas técnicas de análise termogravimétrica (TGA) e calorimetria exploratória diferencial (DSC). As propriedades mecânicas foram avaliadas por análise dinâmico-mecânica (DMA) e ensaios de tração e impacto. A partir dos resultados obti-dos por meio deste trabalho pode-se concluir que o intemperismo envolvendo umidade e radiação UV pode influenciar nos desempenhos térmico e mecânico do compósito de Alumínio/PEBD, porém, foi observado que esta influência não é suficiente para inviabilizar a utilização destes materiais na construção civil, garan-tindo este mercado para o compósito de PEBD/Al

Fiber-Metal Laminate Panels Reinforced with Metal Pins

Fiber-metal laminates (FMLs) are key to modern composite structures and metal-composite coupling is crucial to improve their effectiveness. Cold-metal transfer (CMT) PIN welding, in correlated efforts, has been successfully explored as a metal-composite hybrid joining approach. This work proposes a novel development on FMLs, which consists of introducing metal pins welded by CMT PIN for anchoring their metal and composite layers together. Thus, miniaturized FML panels with different pin deposition spacing and patterns are evaluated with emphasis in drop-weight testing followed by buckling and by means of Iosipescu shear test as complement. They are also subjected to cosmetic and preliminary modal analyses. Besides not adding significant weight, the pins does not make the panels more brittle and their distribution does not imply significant effect in the capacity that the panels have to dissipate impact. The panels with pins exhibit a less catastrophic trend, indicating damage tolerance improvement as significantly higher loads at longer axial displacements in buckling test after impact are achieved. The anchoring effect of the pins is confirmed throughout the shear test results. The pins also significantly increase the damping factor of the panels and the changes in their metal surfaces by the CMT PIN process are considered as irrelevant

Synthesis and Characterization of Polyarylacetylene for Use in the Monolithic Vitreous Carbon Processing

Abstract: In this work, polyarylacetylene (PAA) prepolymer obtained from 1,4-diethynylbenzene was evaluated as polymeric precursor of monolithic vitreous carbon (MVC). The monomer 1,4-diethynylbenzene was synthesized and the PAA prepolymer was prepared with 13, 16 and 19 wt % of nickel catalyst. The best percentage of nickel catalyst considered was 13 wt %, due to the lower molecular weight and polydispersity index and higher carbon yield. The traditional production of MVC is obtained from phenolic and poly(furfuryl alcohol) resins, which require many hours to pyrolyze due to the large quantity of gases generated. Furthermore, the porosity is hard to control using these conventional resins. Polyarylacetylene releases little volatiles due to the polyaddition reaction and the aromatic rings in PAA chain also provide a high thermal stability, therefore the heat treatment could be faster without cracking the carbon material. This would also lower the cost of fabrication of MVC, in addition to the low porosity observed, making this polymer a good matrix for MVC

Estudo dos critérios de falhas em flexão em Compósitos PPS/Fibras de Carbono utilizando elementos finitos

O constante desenvolvimento dos materiais aliado à necessidade de se obter componentes estruturais de alto desempenho como materiais alternativos na indústria aeronáutica, bem como, considerando a aplicabilidade atual dos compósitos estruturais, previsões de falha da estrutura e análise das cargas máximas que as mesmas podem suportar se tornam tópicos fundamentais de pesquisas com a finalidade de garantia da confiabilidade quanto ao emprego dos mesmos em diversas áreas. Considerando que o compósito termoplástico PPS/C – Poli (sulfeto de fenileno) reforçado com fibras de carbono – está surgindo como uma alternativa para a substituição de compósitos poliméricos termorrígidos para aplica- ções específicas e que ainda há escassez na literatura atual de dados relativos à previsão de falhas, este trabalho tem como objetivo realizar uma analise bidimensional do comportamento mecânico do compósito PPS/C sob carregamento estático linear em flexão de três pontos. Neste estudo, foram analisados os critérios de falha de máxima tensão, critérios polinomiais dos índices de força e das relações inversas dos índices de força de Tsai-Wu, de Hill e de Hoffman. Por fim, foram comparados os resultados obtidos a partir do modelo computacional com resultados experimentais obtidos a partir de ensaios de flexão com o objetivo de analisar, avaliar e validar a simulação numérica utilizada