Geometrical characteristics of structural model for 3-D braided composites

It has significant effects on the FEA (finite element analysis) results of the mechanical properties of braided composite to set up a reasonable structural model of 3-D (three-dimension) braided composite. The braided composite after molding was taken as a study object. According to the experimental result and former research, a new model of representative volume elements for FEA of braided composite was proposed. The new model truly reflected the braided manner, coinciding with the actual configuration of the 3-D and four-direction braided composites. On the basis of the new model, the relationship between the braiding parameter and the parameters of unit model was derived and the volume fraction of fibers in this representative volume element was calculated. By studying the geometrical characteristics of the braided composite, it indicates that if the volume fraction of yarn, the radius of yarn bundle and the number of yarns in a yarn bundle are invariable, the pitch length and thickness of composites will increase and decrease respectively with the increase of braiding angle, and the volume fraction can reach as much as 68% theoretically.