The protective vest is an important accessory to absorb impact energy and stop bullets from penetrating the body. Many modern vests are made by polymer matrix composites reinforced with kevlar, glass, and carbon fibers. The presence of water increases the friction between the bullets and the fibers and, as a result, increased the yield of the fabric. The shear thickening fluid (STF) is composed of silica particles dissolved in the liquid phase (e.g., polyethylene glycol). Silica particles are about a few nanometers in diameter. In equilibrium, the liquid phase is filled with colloidal hard particles. At high shear rates, hydrodynamic forces overcome intrusive repulsive forces. So after collision, the colloid particles of the material harden. In this study, experimental and numerical studies of impact on two and four layers of KFLF dipped with STF liquid with different percentages of nanosilica percent were investigated. Numerical modeling was performed with AutoDyn software. By comparing numerical simulation and experimental, good agreement between results of the ballistic limit is obtained. پرونده مقاله