Structural Analysis of 3-D Braided Preforms for Composites Part I: The Four-step Preforms

Abstract

Three-dimensional (3-D) braiding technology using high-performance fibres for advanced composite structures is receiving great attention as a result of the outstanding mechanical and thermoelastic properties of the materials produced. There are now mainly two groups of 3-D braiding techniques, namely, the four-step and the two-step processes. The objective of the research reported in this paper was to study and analyse the preform structures. In this part, theoretical models for the four-step braided structures are established. Structural geometries of the preforms are analysed and discussed in accordance with these theoretical models. Mathematical relations among the structural parameters, such as the fibre orientation, yarn-volume fraction, and preform contour sizes, as well as their dependence on machine-operating conditions, are derived. The extreme values of the parameters due to geometric constraints under the jamming conditions are also analysed and determined. These extreme values dictate the limiting conditions in operation. The good agreement between the experimental observations and the theoretical predictions confirms the validity of the models developed.