Meso-scale modeling of 3-D four-directional braided composites

Based on the motion of yarn carriers on the braiding machine bed, the spatial configuration of interior yarns was analyzed in detail, and a meso-scale model of 4-step three-dimensional (3-D) braided composites was established. In this model, the cross-section deformation, the contact of fiber bundle and the bended centerline due to the mutual squeezing in the braiding process were taken into account. In addition, the structural geometry of the composites was analyzed and the mathematical relationship between the braided parameters and the structure of the unit cell was obtained. The results show that the hypotheses that axis of fiber bundle is curve inside the composites and the section of fiber bundle is oval at control points are close to the real structure and good agreement can be obtained between the calculated and measured values of the geometric characteristics of braided composite samples. The predicted value of unit cell height show that the maximum error remained at about 3%, in addition, when the braided angle is 19°, 21° and 21.5°, the prediction results are more close to the measured results. It is suitable for modeling of 3-D braided composites, especially the structure of small braided angle. Therefore, the model presents a foundation for the mechanical properties prediction of the composites.