Microstructural modeling of three-dimensionally full five-directional braided composites based on a new multiunit cell scheme

In this study, a new multiunit cell model is proposed based on the microstructure analysis of three-dimensionally full five-directional braided composites produced by four-step 1 × 1 procedures. The new multiunit cell model consists of five kinds of unit cells, namely interior, exterior surface, interior surface, exterior corner, and interior corner unit cells, which are developed by control volume method to characterize the unique microstructure features for different regions of three-dimensionally full five-directional braided composites. The relationships between the microstructure parameters of unit cells and the braiding process parameters are analyzed in detail and the structural parameters of the preform are derived. Especially, the squeezing condition of the yarns in the interior region is studied. Finally, the main microstructure parameters of braided specimens are calculated to validate the effectiveness of the multiunit cell model. Good agreement has been obtained between the predicted values and the available experimental data. In addition, the variation of the volume proportion of five kinds of unit cells to the overall specimen with the number of yarn carriers is discussed, respectively. The effect of braiding angle on the squeezing factor of braiding yarn is analyzed. Results indicate that the presented multiunit cell model can be adopted to effectively predict the microstructure and structural parameters of three-dimensionally full five-directional braided composites.