Multi-scale elastic property prediction of 3D five-directional braided composites considering pore defects

Pore defects are unavoidable in 3D braided composites, and can highly reduce the mechanical performance. In this paper, multi-scale analyses are conducted to investigate the effects of pore defects on elastic constants for 3D five-directional braided composites. A modified Chamis model is proposed to calculate elastic properties of yarns with pore defects and validated by the finite element method (FEM). The representative volume cell (RVC) with pore defects is established to predict elastic constants of braided composites, and results are compared with those by experiments and full-scale conventional model. Also, how voids influence elastic properties of yarns and braided composites are fully discussed. Furthermore, the homogenized full-scale model is developed in order to evaluate the possibility and facility in macroscopic performance characterization of braded composites with void defects. Results show that the analytical model is efficient and accurate in elastic property calculation of yarns. It is proper to predict elastic performance of braided composites by RVC with voids. The conclusion indicates elastic properties of yarns and braided composites are significantly influenced by voids. The full-scale conventional modeling of braided composites with voids is extremely complex and time-consuming, which can be solved by the homogenization method to a great extent.