Abstract: Hole defects inevitably occur in the manufacturing process of braided composites, which directly affect the mechanical properties of braided composites. Based on the open source software TexGen^[1], parametric modeling of the inner cell, face cell and corner cell of braided composites was carried out. In the face cell and corner cell models, the deviation of yarn trajectory in space and the extrusion deformation when subjected to the tightening process are considered. The random function is used to introduce pore units into the matrix of microscopic model at micro scale to simulate dry spots in fiber bundles, and pore units are introduced into the matrix of tri-cell model at micro scale to simulate pores between fiber bundle. On macro scale, a macroscopic homogeneous model with inner cell, face cell and corner cell is established to forecast the macroscopic elastic constants. The results show that: ① The porosity has different effects on the elastic constants of the three types of microcellular models; ② The influence of dry spot pores in fiber bundles on macroscopic elastic properties is greater than that between fiber bundles. With the increase of dry spot porosity P_m, the longitudinal Poisson’s ratio is reduced, while with the increase of porosity P_n between fiber bundles, the longitudinal Poisson’s ratio presents the increasing trend.

Key words: three-dimensional four-direction braided composites, porosity, tri-cell model, multi-scale