Microstructure of 3D Braided Preform for Composites with Complex Rectangular Cross-section

Microstructure of four-step 3D braiding preform with 1 × 1 pattern and complex rectangular cross-sections is studied by means of the control volume method. The complex rectangular configuration refers to the geometrical shape jointed by two or more rectangles together. Following the formation rule of the braiding process, the paths of the carriers are traced, particularly in the joint region where two rectangles join together. According to the formation procedures, three unit cell models, both topological and geometrical, are developed corresponding to the microstructure of the interior, surface, and corner in the joint region. The study shows that, in the joint region, the control volume of the unit cell is a cube in the interior, a hepta-prism in the corner, and a penta-prism in the surface, respectively. In addition, the study is able to demonstrate the difference in the braiding pattern and the spatial orientation of braiding yarns in the unit cells between those in the joint region of a complex rectangle and the corresponding region of a simple rectangle by four-step braiding process.