Structural Analysis of 3-D Braided Preforms for Composites Part II: The Two-step Preforms

Abstract

In Part I of this series of papers, structures and geometries of the four-step preforms were studied and analysed. In this part, an account is given of similar work conducted on the two-step preforms. Theoretical models for both regular and tubular two-step preforms are established with a few assumptions. Structural geometries of the preforms are analysed and discussed according to the theoretical models developed. Mathematical relations between the structural parameters, such as the fibre orientation, yarn-volume fraction, and preform contour sizes, as well as their dependence on operating conditions, are derived. It is found that the preform structures are determined by the constituent yarns, the braiding arrangements, and the process operating conditions. The extreme values of the parameters in the jamming conditions are also discussed. To verify the validity of the analytical models, experimental investigations were also carried out. The experimental results strongly support the theoretical predictions.