In order to predict the mechanical properties of 3 D four-directional braided composites with pore defects more accurately,this essay studied the effects of dry patches in fiber bundles and voids in matrix on the macroscopic mechanical properties of the three-dimensional four-direction braided composites based on the two-scale analysis method. Firstly,generalized method of cells was used to predict equivalent mechanical properties of the fiber bundles at micro-scale. Then,the macroscopic equivalent elastic ...