Criticality of inter-yarn friction in high-performance fabrics for the design of soft body armour

Inter-yarn friction plays a pivotal role in determining the impact resistance of woven fabric based soft armour panels (SAPs). This study presents a comparison of ballistic performance of SAPs made from para-aramid, ultrahigh molecular weight polyethylene (UHMWPE) and poly para-phenylene-2,6-benzobisoxazole (PBO) woven fabrics and demonstrates the importance of inter-yarn friction. Plain woven fabrics were prepared using para-aramid, UHMWPE and PBO yarns and SAPs of constant areal density were produced using multiple layers of these fabrics. It is found that despite lower tenacity and modulus of para-aramid fibres, in comparison to those of UHMWPE and PBO, para-aramid SAP exhibits the lowest back face signature (BFS) owing to the highest inter-yarn friction. On comparing UHMWPE based SAPs made from fabrics with yarns of different fineness, fine UHMWPE yarn based fabric exhibits higher inter-yarn friction owing to more number of crossovers per unit length, which further translates into lower BFS of respective SAP. Therefore, while selecting fibres for soft body armour applications, inter-yarn friction should be considered along with the tensile properties.