Dynamic Response Of Shear Thickening Fluid And Its Application In Protective Structures

The rheological properties of shear thickening fluids with different solid contents wereinvestigated by a rheometer to explore the effects of some rheological parameters andtechnological parameters on the rheological properties, and the shear thickeningcharacteristics were improved by chemical modification. Then the dynamic responsecharacteristics of shear thickening fluids were studied using split Hopkinson pressure barunder different constraint conditions, while the flow behaviors were observed by thehigh-speed camera. Then the impact performance of STF/Kevlar fabric composites wasinvestigated, and some influence factors of impact performance of the composites wereexplored and the fracture of fabrics was observed to analyze the failure modes andprotective mechanisms of STF/Kevlar fabric composites. Finally, shear thickening fluidswere applied to porous materials, and the role of shear thickening characteristics on themechanical properties of porous materials was investigated. The main conclusions areshown as follows.(1) There are many factors influencing rheological properties of shear thickeningfluids, such as solid content, particles type, particles size, particle size distribution,synthesis temperature, dispersion approach and dispersion time. These factors can changethe rheological properties by changing the composition and microstructure of the dispersion.The dispersion with higher effective solid volume fraction exhibits higher viscosity andmore obvious shear thickening phenomenon with lower critical shear rate. Solid content,particle size distribution and gas phase composition have significant effects on the effectivevolume fraction of the dispersion. Hydrogen bonds and electrostatic forces are the internalfactors to affect rheological properties. A silane coupling agent can enhance the interactionsbetween silica particles and PEG200by hydrogen bonds and the electrostatic forces can bechanged by adjusting the PH value to change the rheological properties.(2) Shear thickening fluid exhibits a transition from liquid-like to solid-like during theimpact process. Under the same impact condition, the strain rate of shear thickening fluiddecreases and its dynamic stress increases obviously comparing with Non-shear thickeningfluid. The larger impact velocity, the shorter time required for shear thickening transition. Stronger constraint is beneficial to the appearance of shear thickening behavior. Shearthickening properties are the main factors to improve the shock resistance of shearthickening fluid at lower impact velocity, while density plays an important role in theincrease of dynamic performance at higher impact velocity. Shear thickening transition hasgood reversibility.(3) Quasi-static stab resistance and low-impact performance of STF/Kevlar fabriccomposites are significantly improved compared with neat Kevlar fabric, and shearthickening characteristic can enhance the shock resistance of STF/Kevlar fabric compositesmainly by restricting the movement of yarns. When solid content is up to68wt.%, theinternal friction of STF/Kevlar fabric composites is strengthened mainly by silica particles,while the inter-yarn friction is reinforced mainly by shear thickening behavior when solidcontent is over68wt.%. The impact resistance of fabrics is closely related to the interfacialbond strength between fiber and matrix. Excessive interfacial bonding strength easily leadsto brittle fracture of fabric because of stress concentration, while the fabrics are brokenthrough the extraction of yarns as a result of poor interfacial bonding strength. Tensiledeformation is one of the major causes of the improvement of the impact resistance forSTF/Kevlar fabric composites. The low-velocity impact performance of STF/Kevlar fabriccomposites is influenced by solid content, particle size, dilution ratio and so on.(4) Under the impact of bullet, STF/Kevlar fabric composites have gone through threestages, such as shear fracture, tensile fracture and back tensile deformation. The ballisticperformance of STF/Kevlar fabric composites is better than neat fabric with the same arealdensity, partly because the coupling between the yarns is enhanced by shear thickeningbehavior, and partly because the transition from liquid solid-like to liquid solid-like candissipate more impact energy. The enhanced coupling between the yarns can promote therapid spread of stress waves, leading to more even stress distribution, which can improvethe impact resistance and energy dissipation of fabrics. Particle characteristics are importantfactors in the impact resistance of STF/Kevlar fabric composites, and smaller particles caneasily fill the gap between yarns, which is conducive to the enhancement of inter-yarnfriction.(5) SiO2particles added into the rigid polyurethane foam in the form of a shear thickening fluid can improve the quasi-static and dynamic mechanical properties of thefoams. The mechanical properties of polyurethane foam are improved by changing themicrostructure. Quasi-static mechanical properties of rigid polyurethane foam are mainlyaffected by microscopic structure and internal defects, while the dynamic mechanicalproperties are mainly affected by the density of foam. The addition of shear thickening fluidcan increase the number of cell bodies of the foam, reduce the cell body size, and increasethe thickness of cell wall, and the optimal addition amount is2.5wt.%. Besides, as thefilling phase, the shear thickening fluid can significantly improve the dynamic stress ofopen-cell foam aluminum. At low-speed impact, shear thickening behavior plays thedominant role in the dynamic properties of STF/Al foam composites, while at high-speedimpact, the density of the filling phase plays the leading role in the dynamic properties offoam composites.