Since the creation of advanced knives and firearms with high rates of speed, safety has always been a vital issue for armed forces. A disadvantage of a regular fabric Kevlar is that, although it has an effective resistance against the impact of low-speed bullets, it reveals its weakness in the case of a stab wound and high-speed bullets. Under these circumstances, a new executable technology of fibers that improves the ballistic performance of the materials utilized in body armors is an essential necessity to build high quality and protective vests which are perfectly bulletproof. The purpose of this study is to investigate the physics and concepts of shear thickening fluids and perform a computational CFD simulation of liquid body armors which consist of a combination of polyethylene glycol liquid and nanoparticles of silica. A model of multiphase flow environment with STFKevlar, as a representative of the non-Newtonian shear thickening fluid (STF), is simulated in STAR-CCM+ in order to analyze the behavior of STFs under impact and performance of novel liquid body armors. In the current simulation, Eulerian multiphase flow and volume of fluid (VOF) are applied to generate three discrete regions and determine the volume fraction of each phase including gas, non-Newtonian liquid and solid which represent air, STFKevlar and bullet, respectively. Moreover, dynamic fluid body interactions (DFBI) and overset mesh are utilized to consider the interactions between the regions and forces applied. In this study, the properties of the bullet are based on characteristics of a regular pistol bullet, and it approaches the STFKevlar with the constant speed of 400 m/s. The results show that the non-Newtonian material is initially at equilibrium state and while the bullet approaches the STFKevlar, it acts like a shear thinning fluid. As a high-speed bullet nears the STFKevlar, it absorbs the significant amount of energy that is applied by the bullet. Consequently, the bullet stops penetrating the STFKevlar in a very small fraction of time due to the considerable increase in viscosity. As the shear rate increases over a certain critical value, viscosity increases remarkably which is the main characteristic of shear thickening transition and finally, it reaches to its maximum value of viscosity in approximately 8 × 10−5sec. In addition, a bullet applies a considerable amount of force on any Kevlar due to its high velocity and kinetic energy; however, the high resistant STFKevlar is approved as a high quality and protective vests which stops the bullet in 6 × 10−4sec.
The effect of particle strength on the ballistic resistance of shear thickening fluids