Mechanical properties of three-dimensional braided composites

Recently developed digital element approach, which treats textile composite manufacturing process as a nonlinear solid mechanics problem, was successfully used to investigate the complicated microstructure of 3D braided rectangular preform. The yarns interaction and cross-sectional deformation, which were neglected in traditional topological model, could be analyzed exactly. Results showed that yarns inside 3D braided preform were curvy, which was opposite to the straight-yarns assumption of topological model and, yarns curvature inside the preform, which was very difficult to be explored before both experimentally and theoretically, was investigated numerically. After that, the mechanical properties of 3D rectangular braided composites, such as tensile stiffness, shear stiffness and Poisson ratio were calculated through the volume-average-compliance method. Comparison was conducted for those from the topological model and digital element approach, and topological model was found to underestimate greatly both the tensile stiffness and shear stiffness.