Unit Yarn-Addition Technique and Mechanical Properties of Tapered Three-Dimensional Braided Composites

摘要

Tapered three-dimensional braided composites have been widely used in the aerospace and automotive industries. The traditional manufacturing method is to cut the uniform composites to their final shapes, but this process will unavoidably cause serious damage to composites mechanical properties. This paper introduces the unit yarn-addition technique to prepare tapered braided composites net-shapedly. Yarn trajectories of the surface and the interior yarn-addition units are analyzed. Bending properties in the tapered regions of the unit yarn-addition composites and the cut composites are compared and their failure mechanism is discussed, too. Results show that the braiding rules should not be disturbed after yarn-addition and the distribution of the addition units should be uniform. Yarn orientation degree and yarn length in the surface addition unit are increased. The orientation degree and length of one yarn in the interior addition unit increase, while the other yarn only reverses its orientation direction. Bending properties of the unit yarn-addition composites are higher than those of the cut composites. Yarn breakage is the primary failure mechanism of the unit yarn-addition composites. However, matrix cracking and interfacial debonding are the dominant failure mechanism of the cut composites.