Metodologia para a determinação das propriedades mecânicas de compósitos de poliamida 6.6 reforçados por fibras de vidro longas através da simulação de injeção

Abstract

The use of long glass fiber-reinforced thermoplastic composites has increased considerably in the last years. However, the mechanical properties of these materials are strongly dependent on their microstructure (orientation and fiber length) and, consequently, of the processing conditions used in this material. In the case of processing by injection molding, the high shear rates cause, at the same time, reduction of fiber length and fiber orientation on the flow direction, making the prediction of mechanical properties of the composite a difficult task. In this context, the aim of this work was to present a methodology to calculate the tensile strength of long glass fiber-reinforced thermoplastic composites based only on the virtual microstructure estimated by injection simulation. The theoretical basis of this proposal is the Kelly and Tyson model to calculate the tensile strength of composites reinforced with discontinuous fibers, which was modified to use a probability distribution to represent the fibers lengths, in addition the use of the fiber orientation tensor elements. The proposed method also includes an indirect systematic to determine the interfacial resistance between the fibers and the matrix, and the rupture tension of the fibers too. The proposed methodology was evaluated in the composite of polyamide 6.6 reinforced by long glass fibers (50% in mass), which had its microstructure simulated with the help of Moldflow software, using the RSC and ARD-RSC models to estimate the fibers orientation, in addition to the model of Phelps et al to determine the fiber breakage during the injection molding. The mechanical properties of the composite studied, such as tensile and flexural strength, determined experimentally were compared with the theoretical results predicted by the presented methodology. Finally, the model proposed in this work was used to predict the mechanical strength of an automotive structural component (baluster support), and this result was compared with the experimental data of the mechanical tests performed on this component. The differences between the results presented by the proposed calculation methodology and the experimental results were below 15%. Compared to a traditional metal-framed baluster support, the TRFL composite molded support achieved a mass reduction of 30%.[resumo fornecido pelo autor]