Numerical investigation on tensile behavior of three-dimensional six-directional braided composites

Based on the mesostructure, a parametric finite element (FE) model of the three-dimensional six-directional (3D6d) braided composites was developed considering the real cross-sectional shape of the yarn and its contact relationship. The 3D Hashin criterion and maximum stress criterion were used for failure determination and periodic displacement boundary conditions were imposed on the model to numerically simulate the initiation, propagation and final failure of yarns and matrix damage. The FE model accurately predicts the longitudinal tensile strength of 3D6d braided composites and simulates the progressive damage process associated with the stress-strain behavior. The longitudinal mechanical properties of the 3D6d braided composites decrease with increasing braiding angle, while increasing the fiber volume fraction leads to enhancement of these properties. Furthermore, the change rate of longitudinal mechanical properties with braiding angle is relatively stable, and the influence of fiber volume fraction on longitudinal properties decreases with the increase of braiding angle. For the damage mode, the increase of braiding angle makes the damage of braiding and sixth-directional yarns gradually change from single direction to multiple directions, and the decrease of fiber volume fraction makes the damage of braiding and fifth-directional yarns at the peak stress more serious.