Application Of Shear Thickening Fluid On Soft Stab-resistant Body Armor

Recently, the individual protection consciousness increases consequently with the terrorist threat throughout the world, so protection becomes a worldwide problem. Because the use of firearms is controlled very strictly in China and many other countries, but the threat from dagger and bayonets can not be controlled, the research and development of stab-resistant materials is becoming a focus work. To solve the contradictions between performance and flexibility of the conventional stab-resistant protective materials, in this thesis, we proposed to impregnate UHMWPE and Kevlar with different yarn density into shear thickening fluid (STF), so that a kind of novel and flexible stab-resistant material with excellent performance was prepared.In this paper, STF was prepared by dispersing silica particles into polyethylene glycol (PEG) in a blender using the mechanical mixing method. The density, particle size, morphology and microstructure of SiO₂ were characterized and analyzed. Also, the rheological behavior and the factors such as silica mass fraction, molecular weight of PEG and particle size which affected the behavior were studied on rheometry. The Shear thickening mechanism was mentioned, too. STF-UHMWPE and STF-Kevlar composites were prepared by impregnating STF which had been diluted by ehanol. Then the neat fabrics and STF-treated fabrics were done thickness, flexibility and quasi-static knife-resistant tests. The factors which affected the basic performance and knife-resistant performance such as STF dilution ratio, particle concentration, molecular weight of PEG, particle size and the yarn density of the fabric were analyzed. The surface morphology and microstructure of the undamaged and thorn mouth place to the composite materials were characterized by video microscope and scanning electron microscopy. What's more, the related mechanism of knife-resistant was raised. Finally, the properties of the dynamic tests against knife and tests against spike including both quasi-static and dynamic were inferred according to the relevant theory of the bullet-proof study. The results were showed as follows:(1) According to the analysis of XRD and FTIR, Silica powders were amorphous solid particles, what's more, the bond was created between SiO₂ and PEG. Density measured by proportion bottle method, size and TEM analysis showed that, to different particle size of SiO₂, the density, size distribution and single dispersion were different, too.(2) Rheological behavior showed that, SiO₂/PEG system had good shear thickening performance. Silica mass fraction, molecular weight of PEG and particle size can have a certain effect to the rheological behavior. Viscoelastic behavior was observed during the dynamic rheological tests of STF. Reversible research showed that, the system had reversible shear thinning and shear thickening phenomenon. Through"clustering"theory, the shear-thinning and the shear-thickening behaviors of the dispersion can be explained.(3) Thickness, flexibility and quasi-static knife-resistant tests showed that after the fabric was treated by STF, thickness was increased and flexibility was dropped of STF-composite material, while its resistance to knife threats was better than the neat fabric under the equal areal density. The factors such as STF dilution ratio, particle size, particle concentration, molecular weight of PEG and the yarn density of the fabric affected the anti-stab performance with different degree.(4) The undamaged images of SEM showed STF had already impregnated into the surface and inside of the fabric successfully. Video microscope and SEM illustrated fiber fracture state of the thorn mouth place was different. For the neat fabric, the fibers were more loose, with some filament splaying of the ends, while fiber was comparative tidy and showed filament kinking near the broken ends for the STF-composite material. The knife-resistant mechanism showed that the main fracture of the sample was cutting damage.(5) According to the relevant theory of the bullet-proof study, the properties of the dynamic tests against knife and the tests against spike including both quasi-static and dynamic were inferred as follows: When the knife or spike contacted to the fabric surface, the shear rate was beyond the critical shear rate of STF, which resulted in the shear thickening phenomena of STF happen, so that the resistance of both knife and spike to STF-UHMWPE composite fabric would be enhanced. What's more, the anti-spike performance was enhanced better.