Response of ZnO nanorod-modified multilayer aramid fabrics with varied thread densities to sequential ballistic impacts

This work addresses the critical challenge of enhancing ballistic resistance while preserving the flexibility of body armor via the fabrication of ZnO nanorod grown aramid fabrics. ZnO nanorods were grown in situ on plain-woven aramid fabrics with low (P8: 8 ends/cm), medium (P9: 9 ends/cm), and high (P11: 11 ends/cm) thread densities. We systematically explored the coupled effects of fabric density and nanomodification under sequential multi-angle ballistic impacts (6 shots at angles of 0°, + 30°, and − 45°). The results demonstrate that ZnO nanorods substantially increase inter-yarn friction as well as tensile and tear strengths, with only a minor impact on fabric flexibility (increase in bending length < 12%). Notably, the modified medium-density fabric (P9-Z-45L) achieved the optimal performance under six consecutive impacts on a single specimen: its average back face signature (BFS) decreased from 33.45 mm to 23.77 mm, with no penetration observed across all six shots. In comparison, the modified high-density fabric (P11-Z-37L) exhibited a limited BFS reduction of 13.88% and experienced complete penetration under oblique impacts with angle of -45°. Further analysis reveals that the nanorods promote energy dissipation through mechanical interlocking, enhanced yarn engagement, and constrained fabric deformation, which collectively improve energy absorption capacity. This study provides a density-dependent design strategy for flexible, high-performance body armor.