Effective elastic properties and stress distribution of 2D biaxial nonorthogonally braided composites

Due to the interlacement of tows, the architecture of braided composites is complex, especially for the nonorthogonal braid in which the tow has various cross sections along the towpath. The microscopic mechanical analysis is highly sensitive to the geometric architecture, which causes great difficulties for the research on material behavior of nonorthogonal braid. In this article, a finite element model has been proposed to investigate the effective elastic properties and stress distribution of 2D biaxial nonorthogonally braided composites. This research was conducted for two kinds of 2D biaxial braid, 1 x 1 and 2 x 2, using a parallelogram repeated unit cell that is suitable for the description of stress distribution under different load conditions. The differences between 1 x 1 and 2 x 2 in effective elastic properties and stress distribution were discussed. The effect of braid angle on the mechanical properties was also studied. The result reveals that 2 x 2 has greater in-plane Young's modulus than 1 x 1 with the same tow, fiber volume ratio, and braid angle, although the situation of the out-plane Young's modulus is on the contrary.