The effects of the weight fraction (concentration) and silica particle size on steady and dynamic rheological responses of shear thickening fluids (STFs) and the quasi-static (QS) penetration resistance of Twaron®/STF composites have been investigated. The STFs have been made by mechanically dispersing 12 or 60 nm silica particles in polyethylene glycol with molecular weight of 400 gr/mol at three different concentrations. Rheological results indicate that with the increase in the concentration of silica in the STF, the critical shear rate (onset of shear thickening) diminish, the initial, critical, and ultimate viscosities increase and the slope of the shear thinning and shear thickening regions tend to be more steeper. Regarding STFs with larger particle sizes, critical shear rate, the initial, critical, and ultimate viscosities as well as the viscoelastic modules diminish. Addressing the Twaron®/STF composite, the increase in STF concentration and reduction in the silica particles size contribute to considerable increase in the puncture characteristics. The most noticeable puncture characteristics turn out in the case of 35 wt. % STF/Twaron® composites containing 12 nm particles in which the maximum bearable load and the maximum absorption energy are nearly 3.6 and 2.3 times larger than those of the neat Twaron®.
