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Development of liquid armor materials and rheological behavior of shear thickening fluids (STFs)
Colloidal dispersions have been extensively used in many industrial applications such as cosmetic, paint, cement, lubricant and ceramic. Shear thickening is non- Newtonian flow behavior often observed in concentrated colloidal dispersions as an increase in viscosity with increasing shear rate or applied stress. Shear thickening fluids (STFs) exhibit fluid and solid-like properties depending on the shear rate and thus can be used in a variety of applications. In the present study, STFs have been synthesized with various weight fractions of silica nanoparticles in polyethylene glycol (PEG)/ethyl alcohol by mechanical mixing method. The steady and dynamic rheological behavior of shear thickening fluids (STFs) was investigated with rheometer. STFs thermal properties were investigated through thermogravimetric analysis. STFs have been used to improve the performance of Kevlar woven fabrics for protective applications in ballistic and stab. STFs/Kevlar fabric composites have been prepared with different impregnation techniques to evaluate the effects of the STFs. The ballistic performance and stab resistance of STFs impregnated Kevlar fabrics were investigated. Rheological measurements revealed the shear thickening effect of silica nanoparticles/PEG systems depending on the shear rate. In dynamic experiments, the strain thickening behavior was found at critical combination of strain amplitude and frequency. The viscous Gï‚¢ï‚¢ modulus values were found to be greater than the elastic Gï‚¢ modulus. The elastic Gï‚¢ and the viscous Gï‚¢ï‚¢ modulus values were found to increase when the strain amplitude is kept constant and frequency is increased. The same strain thickening behavior was also found when the frequency was kept constant and the strain amplitude was increased. The puncture resistance of STFs/Kevlar fabric composites exhibited significant improvements as compared to the neat Kevlar targets. Based on the SEM results, STFs were uniformly impregnated over the entire surface on the Kevlar fabric and Kevlar fabrics completely coated with STFs. The ballistic test results revealed STF/Kevlar fabric composites have potential to obtain liquid armor materials.