Investigation of the stab resistance mechanism and performance of uncoated and SiO2 coated high-performance aramid fabrics

Surface coatings on the fabrics can enhance protective properties of flexible body armors. It is known that the application of coating increases inter yarn friction, however, detailed mechanism of knife-yarn interaction in coated and uncoated fabrics is not fully understood yet. This study investigates in detail the knife-yarn interaction at individual yarn level and role of improved inter yarn friction in enhanced stab resistance of woven aramid fabrics deposited with SiO2 coating. The coated fabric exhibited an increase of 115% in the knife penetration resistance compared with uncoated fabric due to increase in inter yarn friction. The coefficient of friction increased 29% after coating. The video graphicanalysis performed during quasi static stab resistance revealed important insights into the knife to yarn interactions. The filaments within the yarn in the uncoated fabric interact individually with the knife, undergo sequential cutting of filaments and offer less resistance to knife penetration. On the other hand, filaments within the yarn in the coated fabric were found to interact collectively, as cohesive assembly of fibers, undergo simultaneous cutting offering greater resistance to the penetrating knife. The results of yarn pull out, yarn sliding, single yarn cut resistance and single yarn strength tests confirmed that improvement in the stab resistance was attributed mainly to the increased inter yarn friction after coating the fabric while intrinsic properties of the yarn were not altered. The findings of this study will be helpful in the development of protective clothing with improved stab resistance.