| Shear thickening fluid (STF) is a kind of non-Newtonian fluids, normally being concentrated colloidal suspension. Its apparent viscosity changes dramatically when a high impact is loaded, and even transforms from fluid state to solid-like state. However, it will recover as soon as the load is ceased. Due to its reversibility and shear thickening effect, STF has a great potential in many application fields such as protection or shock absorption. In the thesis, the influences of rheological properties of shear thickening fluids have been systematically studied via stress controlled rheometer. Furthermore, shear thickening fluids, comprised of the dispersed phase (nano-SiO2) and the dispersion medium (polyethylene glycol, PEG), have been applied to impregnate UHMWPE fabrics. The defensive property of STF/UHMWPE composrtes has been studied through stab experiments and the protective mechanism has been explored.Nanoscale SiO2powder easily accumulates because of its high surface energy. In the second chapter, the silane coupling agent KH560has been used to modify nano-SiO2of various diameters. Different kinds of STF were prepared by dispersing nano-SiO2in PEG via mechanical stirring and ultrasonic dispersion. Moreover, the rheological properties and influences of STF were studied. The results showed that applying KH560to modify nano-SiO2particles could achieve powder with less aggregates. The results of steady shear experiments have shown that mass fraction of the dispersed phase, the particle size and the medium type have influence on the rheological behavior of STF. More specifically, STF becomes more viscous with higher nano-SiO2content; the suspensions made from modified nano-SiO2of the average diameter of12nm have greater shear thickening amplitude in the tests; compared with nano-SiO2/PEG200system, the shear thickening phenomenon of nano-SiO2/PEG400system is more apparent. The results of rheological experiments have shown that the reversible shear-thinning and shear-thickening behavior appears in all colloidal suspensions with high content of nano-SiO2, which could be well explained by "clustering" theory.The high mobility of STF under normal state will cause leakage when using it into actual applications. In the third chapter, a new kind of dispersion medium has been produced by using Diphenyl-methane-diisocyantae (MDI) to modify PEG. Moreover, the rheological properties of suspensions were studied by stress controlled rheometer and the influences were analyzed as well. The results of dynamic tests have shown that with higher frequency, the critical stress and the viscosity becomes larger and lower, respectively; the thickening behavior becomes more obvious with increasing nano-SiO2content; by applying nano-SiO2particles of smaller size, the viscosity of STF gets higher and the thickening range becomes wider; shear thickening behavior is observed in both nano-SiO2/PEG systems and nano-SiO2/PEG/MDI systems, but the latter has higher viscosity.Research of stab-resistant materials carried out in and out of the nation mainly focuses on submicron particles. As a result, there are relatively few studies on suspensions using nano-powder as the dispersed phase. In the fourth chapter, the defensive properties of STF/UHMWPE composites have been investigated through stab experiments and the influences of components of STF on stab-resistant properties of STF/UHMWPE fabrics have been discussed. Fabrics impregnated with suspensions which has been made from KH560-modified nano-SiO2(diameter:12nm) have better stab resistance. After the test, only a small quantity of yarns has been pulled out and the penetration depth is merely5.5cm. Additionally, the composite is not heavily destroyed. Compared with pure UHMWPE fabrics, STF/UHMWPE composites contained higher nano-SiO2content or used PEG400as the dispersion medium show better performance in stab experiments. In conclusion, with higher thickening viscosity, the STF impregnated UHMWPE fabrics have better stab-resistant property. |
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