Net shape preparation and bending properties of tapered three-dimensional braided composites

Abstract

The yarn-reduction technique and the yarn-addition technique were introduced to net shape prepare tapered three-dimensional braided composites. Considering that the processes of yarn reduction and yarn addition were mutually inverse, this paper mainly shed light on the former. Two types of yarn-reduction process, the column yarn-reduction process and row unit yarn-reduction process, were discussed in the architectures of preforms thus formed and bending behaviors of corresponding composites. Results show that the principle of these two techniques is that the braiding rules should not be disturbed after yarn reduction or yarn addition. Orientation degrees and lengths of some rearranged yarns are increased in the second step after yarn reduction, whereas the other rearranged yarns only reverse their orientation directions, then the yarn trajectories are the same as before yarn reduction in subsequent steps. Bending properties of the row unit yarn-reduction composites are slightly higher than those of the column yarn-reduction composites and significantly better than the cut composites. The primary failure mechanism of the yarn-reduction composites is yarn breakage, while the dominant failure mechanisms of the cut composites are matrix cracking and interfacial debonding.