Recent developments in shear thickening fluid-impregnated synthetic and natural fiber-reinforced composites for ballistic applications: a review

The main purpose of body armors is to restrict the ballistic impact (bullet velocity ~ 300 to 500 m/s). The conventional rigid body armors are typically consisting of synthetic fibers (SFs) like Kevlar, but these armors are too bulky, stiff, not comfortable, and lack extremities of body protection. But technological advancement inspired researchers to impregnate SFs with shear thickening fluids (STFs) or dilatant materials to develop advanced body armors with better protection, lightweight, and flexibility. The STF is nanosuspension which absorbs a significant amount of impact energy and hence can be utilized to improve the impact performance of fibers. This review is intended to provide a brief overview of single-phase and multiphase STF with additives like silicon carbide and boron carbide nanoparticles to attain better thickening effect compared to single-phase STF. Moreover, the double-shear thickening properties with ionic liquids, role of charged particles, and pH of dispersion medium are found very promising to scale-up the properties of STF in future. The article covers the advancements in STF-impregnated SF and natural fiber (NF)-reinforced composites for ballistic applications. However, the NFs have better capability to retain STF for longer period compared to SFs due to their unique chemical structure and the presence of surface voids and ridges in the fibers. But, mechanical properties of SFs are much better than NFs. Therefore, to develop commercial flexible body armors based on STF-impregnated NF composites, further research is required to attain the same ballistic impact resistance capability as demonstrated by the STF-impregnated SF composites.