The analytical characterization of 2-D braided textile composites

An analytical model based on the unit cell was developed for the prediction of the geometric characteristics and three-dimensional (3-D) engineering constants of 2-D braided textile composites. The crimp yarn angle and the fiber-volume fraction were obtained from the geometric model. The elastic model utilizes coordinate transformation and the averaging of stiffness and compliance constants on the basis of the volume fraction of each reinforcement and matrix material. Seven different fabric architectures have been fabricated and tested by tensile loading to verify the model. The classical thin laminate theory has also been applied to the braided composites in order to compare the predictions with the averaging method. Although the two analytical approaches are well correlated with experimental results, the averaging method is more accurate when the braider-yarn angle is small or when the bundle size of axial yarns is much larger than that of the braider yarns. Parametric studies have been conducted to investigate the effects of the braider-yarn angle and the axial-yarn content to the elastic properties of the composites. The results are demonstrated in the form of property maps for selected moduli and Poisson's ratios.