INVESTIGATION OF YARN PULLOUT AS A MECHANISM OF BALLISTIC PERFORMANCE ENHANCEMENT IN SILICA NANOPARTICLE-IMPREGNATED KEVLAR FABRIC

Impregnating Kevlar fabric with silica nanoparticles is known to augment its mechanical properties, especially under shear deformation. Silica nanoparticle-impregnated Kevlar (SNK) fabric could therefore display improved ballistic performance. In this study, firstly, the ballistic performance of SNK with various percentages by weight of nanoparticle addition and number of layers is investigated utilizing compressed air gun experiments. A colloid-based process is used to impregnate spherical silica nanoparticles having 80-100 nm diameter into Kevlar 29-based K745 style plain woven fabric in a dry state. It was found that the addition of nanoparticles provided about 17.3 % mass advantage (owing to three fewer layers) for the 40 wt.% SNK over neat Kevlar for the non-penetrative case. The area of the damaged zone also showed a strong positive correlation with the kinetic energy absorbed at higher treatment levels. Further, SEM imaging revealed that at higher treatment levels the nanoparticles tend to agglomerate in the interstitial spaces of yarn crossover points. This indicated that the nanoparticles restrict yarn mobility and could improve inter-yarn friction, contributing to the engagement of secondary yarns away from the primary impact zone in the impact mitigation mechanism. In order to understand this mechanism better, yarn pullout tests are conducted on neat and treated fabrics under various conditions. Quasistatic and dynamic loading for in-plane and out-of-plane yarn pullout configurations are examined using customized experimental rigs. Factors such as yarn direction, lateral tension, pullout rate, nanoparticle size, shape, material and treatment level are being considered. For each case, the pullout force versus displacement history is recorded and critical features are extracted. In addition, digital footage is used to analyze pullout kinematics. It is noted that the peak pullout force increases with nanoparticle addition until a threshold treatment level is reached. For a given fabric style and weave, an optimal nanoparticle type and treatment level helps maximize peak pullout force and inter-yarn friction. Coefficients for linear, quadratic, and exponentially decaying sinusoidal fitting functions for various pull-out regimes are calibrated to model yarn pull-out behavior vis-a-vis the treatment parameters. Further analysis of the yarn pullout mechanisms is underway to better understand the ballistic performance enhancement displayed by SNK. It is anticipated that nanoparticle treated flexible armors would not only enhance ballistic protection, but also be amenable to integration with multifunctional capabilities such as wearable electronics, wound coagulation, or smart camouflage.