Analysis of 2D triaxial flat braided textile composites

This paper is concerned with the development of an analytical model for the calculation of the effective linear elastic stiffness of a 2D triaxial flat braided composite (2DTBC) and the effect of initial unintended microstructural imperfections on the calculated stiffnesses. A representative unit cell (RUC) of the braid architecture is first identified along with its constituents. Tow geometry is represented analytically taking account of tow undulation. Each tow is modeled as a transversely isotropic linear elastic solid and the contribution from each tow to the RUC elastic stiffness is obtained by volume averaging, taking account of the volume fraction of each constituent. Predictions of the elastic constants are compared against experimental data and a fully 3D finite element computation based on the RUC. Effects of the bias tow angle, the angle uncertainty and, the bias tow undulation magnitude on the elastic constants are examined by considering composites with bias tows at 30° and 60°. This latter part, thus, examines the effect of microstructural imperfections on the elastic stiffness of 2DTBCs. It also serves as a tool to assess the most significant parameter that affects composite stiffness.