Spacer fabrics are considered by many to be ideal for cushioning applications. They are often warp knitted, have a face layer, a back layer, and an internal spacer layer. The spacer yarns are typically monofilaments that connect the two outer layers to form a three-dimensional structure. They are already used in applications such as car seat padding, for vibration reduction, and as breathable panels in apparel.
Twelve sample spacer fabrics were prepared by Liu et al. (2012), with thicknesses ranging from 5.64 to 10.62 mm. The spacer layer was knitted with polyester monofilament of 0.2 mm diameter for eleven of the samples and 0.16 mm diameter for the twelfth. They found that filament coarseness is a significant variable, with coarser monofilaments providing more protection. The spacer yarn inclination was found to significantly affect impact behavior. An optimum structure is needed: not too vertical, nor too inclined. Comparisons between spacer fabrics and other protective materials were not obtained. Subsequent research (Liu, Au, & Hu, 2014a, 2014b) involved a hemispherical test surface and impact energies up to 50 J. This revealed greater complexity in understanding both impacts and the effectiveness of spacer fabric as a protective material.
Chen, Lai, Sun, Zhao, and Chen (2017) analyzed the compressive deformation mechanism of a spacer filament with the objective of providing guidance for designers of spacer fabrics. They divided the compression process into four stages: the stiff stage, the elastic stage, the restful stage, and the ineffective stage.
Zhao, Long, Yang, and Liu (2017) have focused attention on weft-knitted spacer fabrics because of the potential for seamless shaping of impact protectors. Sixteen samples of weft-knitted spacer fabrics were knitted with varying spacer yarn patterns, filament diameters, and fabric densities. Thicknesses ranged from 2.7 to 6.4 mm. Their work is concerned with cushioning rather than dynamic impact protection, but the approach is one that has great potential for producing shaped panels for protection.
Nayak et al. (2017) considered the potential of using spacer fabrics as alternatives to foam padding. Three samples were knitted. Fabric A had mercerized cotton and elastane for external layers, with ballistic nylon as the internal layer. Fabrics B and C both had Dyneema and Elastane external layers and a Dyneema internal layer, but knitted with different structures. These were compared with closed cell foam obtained from a rugby clothing manufacturer. Their conclusion: “the flexible 3D knitted textile structures can provide equivalent level of impact protection achieved by the commercial foam used in the rugby clothing. The flexible knitted structures can also provide higher level of comfort to the players compared to the commercial foam as indicated by higher air permeability and lower thermal resistance and water vapour resistance.”
The research into spacer fabrics raises expectations that impact protection is feasible using these materials. The papers also show that suitable properties need to be engineered during the design process. Spacer fabrics designed to permit permeability and cushioning may provide little protection, as experiments with commodity spacer fabrics undertaken by the writer have demonstrated. There is also scope for composite materials, and reference has already been made to the Deflexion S-range: polyester spacer fabrics impregnated with a silicone covering resulting in permeable, flexible protective materials. Zhou et al. (2013) have also developed this approach by making use of microgels.
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