Low‐Velocity Impact Properties and Failure Modes of Knitted Tubular Shape Memory Polymer Composites Inserted With Helical Yarns

Tubular knitted‐fabric reinforced shape memory polymer composites (SMPCs) have gotten much research attention due to their excellent smart response and large recoverable deformation capacity. However, there is a lack of research on the quasi‐static and low‐velocity impact mechanical properties of knitted tubular shape memory composites. In this work, the weft‐plain knitted fabrics tubular composites inserted with single and double helical yarns were fabricated. The mechanical properties, energy absorption, and damage modes of knitted tubular composites under axial/transverse quasi‐static compression and low‐velocity impact were investigated, respectively. The results show that the introduction of helical yarns greatly improves the mechanical properties of knitted tubular composites and enhances the structural stability. As compared to tubular composites without helical yarn, the quasi‐static axial loading force and transverse loading force of knitted tubular composites with double helical yarns are increased by 12.36% and 61.79%, respectively. Furthermore, under low‐velocity impact loading, the knitted tubular composites with double helical yarns have larger impact force, more elastic absorption energy, and less damage than other knitted tubular composites. The stress transfer and damage modes between the knitted tubular composites without helical yarn and with helical yarns are different. The knitted tubular composites under quasi‐static loading have similar damage modes to the composites under low‐velocity impact loading.