Effect of Fabric Topology and Axial Yarn Condition on the Compressive Properties of 3D Stepwise Rotary Braided Composites

Three-dimensional braided composites have become one kind of critical engineering material for applications in extreme environments. The 3D stepwise rotary braiding process is one vital technique for manufacturing preforms with high efficiency and flexibility. However, the fabric topology is decided by the combination of switch rotation directions, which affects the mechanical properties, and the full carrier configuration results in a loose four-directional structure which is supposed to be improved by adding axial yarns. Therefore, experiments are carried out to illustrate the effect of fabric topology and axial yarn condition on the compressive properties of 3D stepwise rotary braided composites. Samples with three types of fabric topologies named Type A, B, and C are prepared under four axial yarn conditions including no axial yarn addition, 12K axial yarn addition, 24K axial yarn addition, and 36K axial yarn addition, which are fabricated with braiding angles of 20°, 30° and 40°. Longitudinal and transverse compression tests are conducted, and the morphology is observed. It shows that the braiding angle has more influence on the longitudinal compressive properties than transverse compressive properties, and the effect of fabric topology and axial yarn condition depends on the braiding angle. The fabric topology affects a lot on the longitudinal compressive properties when the braiding angle is small, resulting in a gap of up to 40%. The longitudinal compressive properties are improved significantly by adding axial yarns especially for the composites with large braiding angles, making the strength more than double. With the increase in axial yarn size, the strength increment gradually decreases while the modulus declines after a certain size for smaller braiding angles.