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.