RESUMO O presente trabalho aborda a determinação das constantes elásticas efetivas de materiais compósitos estruturais de uso aeronáutico por meio de ensaio de vibração. O experimento foi conduzido em um aparato apropriado com interferômetro a laser. Inicialmente, foi realizado um ensaio de vibração do tipo livre para obtenção das frequências naturais intrínsecas à placa de compósito híbrido de alumínio aeronáutico com tecido prepreg de fibra de carbono/epóxi (CARALL). Do mesmo modo, verificou-se por meio deste método, o alumínio 2024 T3 que é uma liga metálica que pode ser aplicada em aeronaves. Tanto o alumínio quanto os compósitos foram modelados em aplicativo computacional (ANSYS) onde por meio do método de elementos finitos obtiveram-se frequências relacionadas aos seis primeiros modos de vibração. O alumínio aeronáutico apresentou uma maior precisão entre os materiais analisados em relação as suas frequências naturais. Em relação as constantes elásticas, a liga de alumínio 2024 T3 apresentou um módulo E1 de 71,3 GPa e um coeficiente de Poisson de 0,31. As constantes elásticas do CARALL foram determinadas como solução de um problema de otimização computacional descrita em linguagem própria contida em uma sub-rotina do ANSYS. Observou-se que o módulo de elasticidade principal e o coeficiente de Poisson são próximos dos valores encontrados numericamente pela regra da mistura (70 GPa e 0.3, respectivamente).

ABSTRACT This paper deals with the determination of the effective elastic constants of structural composite materials of aeronautical use by means of vibration test. The experiment was conducted in an appropriate apparatus with a laser interferometer. Initially, a free-vibration mode vibration test was performed to obtain the natural frequencies intrinsic to the hybrid composite plate (aeronautical aluminum lamina’s alternating to carbon fiber/epoxy fabric lamina’s) known as CARALL. Likewise, aluminum 2024 T3 which is a metallic alloy that can be applied in aircraft was verified by means of this method. Both the aeronautical aluminum and the hybrid composite were modeled in a computer application (ANSYS) where, through the finite element method, frequencies related to the first six modes of vibration were obtained. The aeronautical aluminum presented a greater precision between the materials analyzed in relation to their natural frequencies. Regarding the elastic constants, the 2024 T3 aluminum alloy presented an E1 modulus of 71.3 GPa and a Poisson’s ratio of 0.31. The CARALL elastic constants were determined as the solution of a computational optimization problem described in its own language contained in an ANSYS subroutine. It was observed that the main modulus of elasticity and Poisson’s coefficient are close to the values found numerically by the mixing rule (70 GPa and 0.3, respectively).

A low cost and environmental friendly extrusion process of the Polyacrylonitrile (PAN) polymer was viabilized by using the 1,2,3-propanetriol (glycerol) as a plasticizer. The characterization of the fibers obtained by this process was the object of study in the present work. The PAN fibers were heat treated in the range of 200 °C to 300 °C, which is the temperature range related to the stabilization/oxidation step. This is a limiting phase during the carbon fiber processing. The characterization of the fibers was made using infrared spectroscopy, thermal analysis and microscopy. TGA revealed that the degradation of the extruded PAN co-VA fibers between 250 °C and 350 °C, corresponded to a 9% weight loss to samples analyzed under oxidizing atmosphere and 18% when the samples were analyzed under inert atmosphere. DSC showed that the exothermic reactions on the extruded PAN co-VA fibers under oxidizing synthetic air was broader and the cyclization started at a lower temperature compared under inert atmosphere. Furthermore, FT-IR analysis correlated with thermal anlysis showed that the stabilization/oxidation process of the extruded PAN fiber were coherent with other works that used PAN fibers obtained by other spinning processes.

Polyacrylonitrile fiber encompasses a broad range of products based on acrylonitrile (AN) which is readily copolymerized with a wide range of ethylenic unsaturated monomers giving rise to polymers with different characteristics and applications. Such products can be designed for cost-effective, flame and heat resistant solutions for the textile industry, aircraft and automotive markets. In the present work acrylonitrile was copolymerized with vinylidene chloride (VDC) by conventional suspension polymerization process via redox system, with an initial content of 10%/mass of the VDC monomer. The copolymer average molecular weight was obtained by Gel Permeation Chromatography (GPC) and by intrinsic viscosity analysis. To control the polymerization process continuously, qualitative and quantitative analysis of the chloride content in the PAN AN/VDC copolymer structure was accomplished by using X-ray fluorescence and potentiometric titration techniques. A good correlation was found between these two techniques, leading to a straightforward verification of VDC in the polymer structure. The thermal behavior of PAN AN/VDC copolymer was performed by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The results showed that VDC monomers exhibited a nearly stoichiometric reaction with acrylonitrile, copolymerizing about 90% of its initial mass. VDC changed significantly the polyacrylonitrile thermal behavior, decreasing the polymer degradation temperature by about 40-50°C.

O presente trabalho resume os processos de fiação convencionais usados na obtenção de fibras de poliacrilonitrila (PAN). Um breve histórico do desenvolvimento da fibra de PAN é apresentado. A empregabilidade das fibras de PAN está atribuída principalmente ao setor têxtil e aeronáutico (como principal precursora para fibras de carbono). Atualmente, o processo de fiação úmida tornou-se o único meio para produção industrial de fibras de PAN, que emprega o DMF (dimetilformamida) como principal solvente para esta técnica de fiação. Descreve-se um novo método de fiação da PAN que dispensa o emprego de solventes altamente tóxicos. Essa tecnologia inovadora permite fiação por fusão da PAN que pode empregar a glicerina (proveniente da produção do biodiesel) como seu principal plastificante.

This paper summarizes the conventional spinning processes used to obtain polyacrylonitrile (PAN). A brief history of the development of PAN fiber is presented. The employability of PAN fibers is attributed mainly to the textile sector and aviation (as main precursor for carbon fibers). Currently, the wet spinning process became the only means of industrial production of PAN fibers, which employs DMF (dimethylformamide) as the main solvent for this technique of spinning. We describe a new method of spinning of PAN with no need of using highly toxic solvents. This innovative technology enables spinning by melting PAN using glycerin (from biodiesel production) as the primary plasticizer.

Neste trabalho são apresentados resultados de análise térmica para poliacrilonitrila (PAN) plastificada com glicerina. Foram observados os efeitos da glicerina de alta pureza (glicerol) e demais aditivos à base de glicóis na fusão e degradação térmica da PAN pela técnica de DSC sob alta taxa de aquecimento (90 °C/min) e atmosfera inerte. Foi constatado que o glicerol reduziu a temperatura de fusão da PAN de 290 °C para 217 °C. Em uma etapa preliminar foi empregado o método de Kissinger para verificar o efeito da composição química da PAN sob sua degradação térmica. A energia de ativação aparente para o copolímero de PAN foi calculada em 149 kJ.mol-1. Sugeriu-se que a presença do comonômero acetato de vinila (AV) na composição química da PAN proporcionou menor entalpia de degradação (353 J.g-1) em comparação com outros comonômeros constituintes de uma PAN precursora de fibras de carbono (988 J.g-1).

This paper presents results from thermal analysis of polyacrylonitrile (PAN) plasticized with glycerin, where effects from the high purity glycerin (glycerol) and other additives to glycol were studied. Using differential scanning calorimetry (DSC) at high heating rate (90 °C/min) and inert atmosphere, we observed a decrease in the melting temperature of PAN (from 290 °C to 217 °C) owing to the presence of glycerol. The Kissinger's method was used to investigate the kinetics of thermal degradation for acrylonitrile (AN) with vinyl acetate (AV). The apparent activation energy for the copolymer AN/AV was calculated as 149 kJ.mol-1. The AV comonomer resulted in a lower degradation enthalpy for the copolymer AN/AV (353 J.g-1) compared with the comonomers comprising a precursor PAN for carbon fibers (988 J.g-1).