Micro-Geometry of 3-D Braided Tubular Preform

The micro-geometry of three-dimensional (3-D) braided tubular preform is more complex than that of rectangular one, and it is more difficult to analyze its architecture and mechanical properties theoretically as well. Through the advantage of digital element approach for textile technology, 3-D circular braiding process could be simulated dynamically using different parameters like yarn tension, yarn properties, the size of yarn and mandrel, pitch length etc. Yarns in 3D tubular preform were found to be nearly straight when projected onto r – plane, which is similar to those in rectangular preform on x – y plane. And yarns on x – y plane were smooth curvy lines, which could be described quantitatively. Unit-cell at the interior of the preform was isolated out based upon same topology consideration for rectangular preform. But the size of unit-cells and the yarn inclination in them varied with its radial position though their shape and micro-structures are analogous. Three important parameters of unit-cell: braiding angle and fiber volume fraction Vf and yarn inclination angle, were discussed in detail. And digital element approach was found to be quite unique for the exact analysis of the micro-geometry of 3-D braided tubular preform.