(553d) Composites of Electrospun Fibers and Shear Thickening Fluids for Liquid Body Armor

Two major types of existing body armors are: hard body armors, which usually consist of metals and ceramics, and soft body armors, normally containing 20-50 layers of fabrics. However, both types suffer from heavy weight and limited flexibility. Therefore, there has been increasing interest in the development of liquid body armors, which combine shear-thickening fluids (STFs) with the fabric materials, such as Kevlar, to reduce the number of fabric layers needed while providing the same impact resistance [1]–[4]. STFs are fluids that increase in viscosity when experiencing rapid deformation. Incorporating a STF into body armor materials helps dissipate energy from impact and distribute load more effectively. Several studies have shown that such composites demonstrate improved resistance to ballistic, stab, and puncture impacts [4]–[6].

One of the main challenges of existing STF-treated fabrics is their ability to hold the STFs in place. Due to gravity, the STFs inevitably flow downwards, reducing shape stability. In addition, if the pores in traditional fabrics are too large, it is suspected that the STFs would coat the surface of the fibers instead of filling the entire pores, limiting the shear-thickening behaviors in the composite.

In this study, the liquid retention of STF-treated fabrics is improved by using fabrics comprising electrospun ultrafine fibers. The electrospun fibers have smaller fiber diameters, thus higher surface area and smaller interfibrillar spaces for the same amount of fiber, leading to increased capillary forces to sustain the STFs in place against gravity. As proof of principle, a nylon-based fabric is produced by electrospinning, which has relatively high structural stability and is easily wetted and impregnated by the STF. The STF used is silica-based and shows discontinuous shear-thickening, rendering it effective in impact resistance. The STF-impregnated electrospun fabrics are characterized for their shape stability with long-term exposure and break-through pressure tests. The mechanical properties of the composites are measured through both tensile and drop tests, to probe wearability and impact resistance. This work explores the potential for improving the stability of STF-fabric composites for body armors by taking advantages of capillary forces in the fabrics and provides insight into the effects of shear thickening behavior in the performance of such composites.

References

[1] A. Majumdar, B. S. Butola, and A. Srivastava, “Development of soft composite materials with improved impact resistance using Kevlar fabric and nano-silica based shear thickening fluid,” Mater. Des., vol. 54, pp. 295–300, 2014.

[2] C. Zhao, C. Xu, S. Cao, S. Xuan, W. Jiang, and X. Gong, “Anti-impact behavior of a novel soft body armor based on shear thickening gel (STG) impregnated Kevlar fabrics,” Smart Mater. Struct., vol. 28, no. 7, p. 075036, 2019.

[3] S. K. Yeh et al., “Light shear thickening fluid (STF)/Kevlar composites with improved ballistic impact strength,” J. Polym. Res., vol. 26, no. 6, 2019.

[4] R. D. Dombrowski, N. J. Wagner, M. Katzarova, and B. J. Peters, “Development of Advanced Environmental Protection Garments Containing Shear Thickening Fluid Enhanced Textiles (STF-Armor) for Puncture Protection and Dust Mitigation,” in 48th International Conference on Environmental Systems, 2018, no. 183.

[5] Y. S. Lee, E. D. Wetzel, and N. J. Wagner, “The ballistic impact characteristics of Kevlar® woven fabrics impregnated with a colloidal shear thickening fluid,” J. Mater. Sci., vol. 38, no. 13, pp. 2825–2833, 2003.

[6] M. J. Decker, C. J. Halbach, C. H. Nam, N. J. Wagner, and E. D. Wetzel, “Stab resistance of shear thickening fluid (STF)-treated fabrics,” Compos. Sci. Technol., vol. 67, no. 3–4, pp. 565–578, 2007.

Acknowledgement

Funding for this study is provided by the Australian Government Defense Science and Technology Group. We would like to acknowledge MIT Institute of Soldier Nanotechnology for use of facility.