Geometric simulation of holes in preform of four-step 3D braided composite

According to the four-step braiding pattern and the cross-sectional variation of the yarn, the discrete digital element approach for characterizing orientation of the yarn in the preform was proposed. At the same time, Using Visual C++ and SolidWorks API, the software was programmed which can automatic generate the structure of holes extend among yarns within the three-dimension braided preform and calculate their volumes. The holes in the preform, with the braided angle 25° and 35°, the fraction volume of fiber 30% and 40%, and the number of rows and columns 2 × 4 and 3 × 3, were simulated and calculated respectively. The relative error between the simulated and theoretical hole's volume is less than 5%. The results indicated that with the braided angle or fiber volume fraction increasing, volume and area of the holes within the preform became smaller, but the hole's area per volume increased.