On the topological yarn structure of 3-D rectangular and tubular braided preforms

Abstract This paper presents an analysis method for the description of yarn structures in 3-D braided preforms. Initially, the general topology of the yarn structure in the preform is determined on the basis of the braiding procedure alone. Then, from the general topology, unit-cell-like substructures are identified in the preform interior and on the boundary. Thus, the total preform is represented as a structural composition of the unit cells. A full description of the yarn structure topology is necessary for the determination of the final yarn structure after the preform is impregnated with matrix and consolidated into the final shape. In particular, if the final shape is not the same as the initial shape, the yarn structure in the final shape may be obtained by a particular topological mapping procedure. Preforms of rectangular and tubular cross-section braided by the popular 4-step 1 × 1 procedure are analyzed as examples. The topology in the respective yarn structures is described in terms of some physically measurable parameters. It is shown that the topological characteristics in both preforms are the same; only the respective characterizing parameters are determined by the specifics in the respective geometric shapes.