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

The study addresses a gap in understanding how knitted tubular shape memory polymer composites behave under quasi-static compression and low-velocity impact. The authors fabricated tubular knitted-fabric reinforced SMPCs and inserted single or double helical yarns to form different composite architectures. Mechanical properties, energy absorption, and damage modes were evaluated under axial and transverse quasi-static compression as well as low-velocity impact. The results indicate that adding helical yarns improves mechanical performance and structural stability. Compared with tubular composites without helical yarns, the double-helical-yarn composites show increased quasi-static axial and transverse loading forces. Under low-velocity impact, the double-helical-yarn composites exhibit higher impact force, greater elastic absorption energy, and less damage than the other configurations. The paper also reports that stress transfer and damage modes differ between composites without helical yarn and those with helical yarns, and that damage modes under quasi-static loading resemble those seen under low-velocity impact.