Microstructural Design of Advanced Multi-Step Three-Dimensional Braided Preforms

Abstract

The "multi-step" braiding process is introduced as an extension to the four-step braiding process. This process greatly enlarges the possibilities of braid micro-structures. An assumed yam packing arrangement within the braided preform and geometric considerations were used to relate yam orientation to non-dimensional pitch length. Further, study of the fundamental principles of track and column braiding yielded a relationship between track/column shifting sequence and yam orientation, pitch length, and yarn diameter. Coupled via. computer software, these relationships provide a link between design parameters such as preform size, yarn diameter, and microstructure to operating parameters such as pitch length and shifting sequence. Additionally, the volume of yam in a given pitch length divided by that pitch length has been predicted. This supplies a simple method of calculating fiber volume fraction. Experimentally measured yam volume fraction and yarn orientation have shown close agreement with theoretical predictions.