Performance Characterization And Protection Application Of Shear Thickening Fluid

Shear thickening fluid (STF) is a kind of novel functional materials. Its apparent viscosity changes dramatically when a high impact is loaded, and even transforms from fluid-state to solidlike-state. It will recover as soon as the load is ceased. Due to shear thickening effect, this kind of materials is promising in the application of anti-impact protective devices. However, there are still some problems to be solved, such as the preparation of the high-performance STF, the non-rheological properties, STF’s application, and so on. Be aimed at this situation, this dissertation introduces the influencing factors of shear thickening effect, the vertically vibrated surface instability and the protection application of the STF. This research provides important theoretical and experimental basis for the STF and its application.This dissertation developed several series of the STFs, and the rheological behavior was characterized in detail with a rheometer in steady and dynamic measurement, respectively. The influences of dispersing medium’s molecular chain length and the additive’s concentration and molecular chain length on shear thickening effect were investigated. The results were validated in both experiment and fitting model. The STF was prepared by dispersing the nano or micron scale particles into solvents. The rheological properties related to the requirement of application, including shear thickening effect, stability, reversibility and thixotropy, were investigated, and the influence of particle content was also discussed. Based on the power law function and Navier-Stokes equation, two quasi-static models, axisymmetric model and parallel plate model, for STF damper were derivated. In order to investigate the effect of dispersing medium on shear thickening effect, the STFs based on dispersing mediums with different molecular chain lengths were prepared. Three samples were prepared with silica dispersed in different dispersing medium, including polyethylene glycol (PEG)600, PEG400and PEG200. The results indicated that the shear thickening effect was significantly raised with the increase of the molecular chain length of the dispersing medium. The reason was that the increase of molecular chain length could enhance the agglomeration of particles to form large particles clusters. Formation of large particles clusters was helpful to achieve high shear thickening effect. The STFs based on additives with different concentrations and molecular chain lengths were also investigated. The STF samples were prepared with silica and additive dispersed in PEG400. Three types of additives with different molecular chain lengths, PEG4000, PEG6000and PEG10000, were used. For PEG10000, different concentrations, including0,1,3and5v/v%, were selected to study the influences of additive concentrations. The results demonstrated that the shear thickening effect was significantly enhanced with the increase of the concentration and the molecular chain length of additives. The mechanism of enhancement was qualitatively explained with the formation of large particles clusters.The experimental measurement system for the surface instability of the vertically vibrated suspension was established. The vertically vibrated dynamic property of the STF was observed and investigated. A simplified model based on fluid dynamic was proposed. The apparent viscosity of the STF changed dramatically with the applied shear rate, which was a typical rheological property of the STF. Such a rheological property affected the vertically vibrated dynamic property of the STF. Above a critical driving acceleration, the surface instability transformed from the disappearance to the fission of the initial hole, which was produced by applying a finite perturbation to the surface. The time required for the initial hole disappearing could be affected by the driving acceleration, vibration frequency, volume fraction, thickness and the shape and size of the perturbation. The expressions of hydrostatic force and viscous dissipative force were employed to clarify the relationship between the hole disappearance phenomen and shear thickening effect. The fission and spreading followed a hexagonal arrangement. At a higher acceleration, the holes covered the entire surface in a state of disorder. The mechanism for the evolution of the initial hole in the vertically vibrated STFs was discussed.The STF enhanced Kevlar fabrics were developed and the cutting and puncture resistance performance were investigated in experiment. The enhancement mechanism of the STF on the fabrics was discussed systematically. The rheological properties of the STFs were tunable by varying both the dispersing particles (the spherical silica, polymethylmethacrylate, and polystyrene-ethylacrylate particles) and the mediums (EG, PEG200, and PEG600), respectively. The STF reinforced fabrics were tested by both the knife and spike drop tower testing to evaluate their mechanical properties. For the cutting resistance, the particle’s hardness was the dominant factor, while the inter-yarn friction played as the critical role for improving the puncture resistance. The inter-yarn friction was measured by the single yarn pull out testing. In comparison to neat fabric target, the cutting and puncture resistance of the STF-fabric target exhibited significant enhancement. The results of yarn pull-out testing and optical microscope images after the drop tower testing agreed well with the drop tower testing. The enhancing effect was systematically discussed and the improving mechanism was analyzed.