The Preparation And Performance Of Shear Thickening Fluid (STF) And STF/Kevlar Cmposites

Shear thickening fluid is a kind of non-newtonian fluid which often occurs as anabrupt increase in viscosity on increasing shear rate beyond a critica lshear rate. As the keycomponent of a new protective material called lquid armor, STFalso has many importantapplications in damping devices. The investigation of STF’s properities and its influencingfactors is in favor of the preparation of high-performance protective materials and dampingdevices.In this paper, the fumedsilica particles or submicron silica particles were dispersed intopolyethylene glycol (PEG) to prepare different ratios of shear thickening fluid, and therheological properities of STF wasimproved by optimizingthe process ofpreparation.Thesteady-state and dynamic rheological properties of STF, as well as the dynamic response ofSTF under high speed load of the split Hopkinson pressure bar were tested to measure theinfluence of solid content, particle type, particle size and other factors of STF.Meanwhile,the high-speed photographic instrument was usedto analysis the corresponding impactmechanism. Kevlar fabricswere impregnated with STF to prepare STF/Kevlar compositematerials, the next step, composite materials were impacted at low speed to test itsprotective performance. Solid content, areal density and other factors on STF/Kevlarcomposite protective performance were explored. The main conclusions of this paper areshown as follows:(1) Factors as solid content, particle type, particle size and particle size distributionwill affect the rheological properties of STF. Solids content, particle size and particle sizedistribution will affect the effective volume fraction, the higher the effective volumefraction, the higher its viscosity, the smaller the critical shear rate, then shear thickeningeffect is more significant. In SiO2/PEG dispersion system, hydrogen bonding between SiO2particles and PEG and electrostatic interactions between particles are the intrinsic factorsinfluencing rheological properties.(2) Fluid has both elastic behavior and viscous behavior, and they are characterized bythe storage modulus (G’) and loss modulus (G"), respectively. For shear thickening system,G" and G’ increase with shear stress going up, while for non-shear thickening system, G"changes slightly, G’ decreases with shear stress at first, and then increase slightly, theoverall performance is decrease.(3) Shear thickening fluid exhibited sudden increase in viscosity and transformed froma liquid dispersion into a material with solid-like properties during the impact process, thestress wave attenuation effect was also observed. Meanwhile, shear thickening effect hadsignificantly reduced the strain rate, and improved the dynamic stress of fluid.Strongconstraints imposed on STF has increased the dynamic stresses, which was in favor ofshear thickening behavior.As the aperture became greater, the constraint effectofsleevesbecame weaker, fluid dynamic stress decreased in this way.(4)The low velocity impact resistance performance of STF impregnated Kevlar fabricswas improved by increasing the friction and the coupling effect between fibers.There weremany factors influencing the performance of STF/Kevlar composites, such as STF types,silica particle size, solid content and areal density.Solid content affected the shearthickening behavior, on the other hand, particle size and the type of STF affected the fiberfriction. As the shear thickening effect become more significant, thecoupling effect and loadtransfer between fibers will be better, so as toimprove the low velocity impact resistanceperformance of STF/Kevlar composites.