Estudo das propriedades dinâmico-mecânicas e fluência de compósitos epóxi/tecido não-dobrável de carbono produzidos por VARTM e RFI

Abstract

The excellent cost-weigh-performance relationship of polymeric composites compared to traditional materials became a reason to development of advanced materials for structural application such as carbon/epoxy composites, and with that, new processing methods, different resins (matrix) and fabrics (reinforcement) producing. Polymers and their composites present viscoelastic behavior, and so issues such as dimensional stability and long-term resistance must be taken into account when used by aeronautic industry. Dynamic-mechanical analysis (DMA) allows the evaluation of viscoelastic properties, and with creep tests, it is possible to study materials strain as function of time, under constant stress and temperature. In this study, epoxy/carbon NCF composites were manufactured by two techniques: vacuum assisted resin transfer molding (VARTM) and resin film infusion (RFI), and a comparative analysis between both composites was made. Storage modulus, E’, for RFI composite was approximately 10 GPa higher along the glassy region and Tonset approximately 60°C higher than VARTM composite. RFI composite also presented a wider glass transition region (form tan δ curve). These results were associated to the molecular relaxation and higher chain cooperative motion, and to the higher stiffness of RFI composite. Creep strain tests were performed in three different stress levels and temperatures, and VARTM composite presented larger creep strain with time, indicating a weaker interface fiber/matrix and a lower stiffness composite, and corroborating with short-beam shear resistance. Findley and Burger’s model were applied and both agreed well with experimental creep curves. Parameters of each model were associated to composites viscoelastic behavior and they were related to the other results.