Microstructure/property relationships in three-dimensionally braided fiber composites

Three-dimensional braiding is a unique way of manufacturing composite structures directly in their final shapes. In the process, the fibers (yarns) are braided first into a structural preform which is then impregnated with a matrix material and consolidated into the final shape. The purpose of this paper is to demonstrate the analytical link between manufacturing and microstructure, and to properties of braided composites. A descriptive methodology for the yarn skeletal structure in the preform is presented based on the braiding procedure. The yarn skeletal structure so identified preserves the topological character in preforms of any permissible shape. This feature allows the determination of the yarn structure in the consolidated composites whose shape may be distorted during consolidation. From the final yarn structure, local and global properties of the composite can be obtained through a modeling procedure. Structural shapes braided by the four-step 1 × 1 procedure are used as examples; numerical results of thermomechanical properties in variously braided preforms are presented in explicit terms of the braiding parameters.