Hollow Three-Dimensional Knitted Structure Reinforced Composites

Abstract

This chapter describes a novel kind of 3D knitted spacer structure reinforced composites of adaptive stiffness which can be used as cushioning material for human body protection. 3D knitted spacer structure is a typical hollow structure consisting of two separate outer layers joined together but kept apart by spacer monofilaments. This special structure makes the fabric lightweight and flexible. Spacer fabrics can be developed to have cushioning feature with three distinct stages under compression, i.e., linear elasticity, plateau, and densification. To enhance the impact protective performance of the hollow knitted spacer structure, a novel impact hardening polymer (IHP) was synthesized to reinforce the spacer structure. The IHP showed a storage modulus at a higher shear strain rate of 6000 times as that at a lower shear strain rate. The impact protective properties of the developed hollow 3D knitted structure reinforced composites were assessed via drop-mass impact tests under both the flatwise and hemispherical forms. It was found from the flatwise impact tests that the developed hollow composites have adaptive initial stiffness subjected to different impact velocities. Their energy absorption capacities were significantly improved compared to the original spacer fabric. The hemispherical tests proved that the developed composites can tend to rigid instantly upon impact and shunt the impact force to a larger area. The composites were also tested according to the European Standard BS EN 1621-1:1998 to assess whether they are suitable for human body protection and compared with the results of some typical commercial hip protectors. The results showed that the novel composites possess superior impact protective performance without compromising of comfort.