Abstract
The ballistic resistance of high-strength fabrics improves upon impregnation with Shear Thickening Fluids (STFs). The performance of such STF treated fabrics depends on the rheological properties of the STF which in turn are governed by the physicochemical properties of the STF. The present study utilizes rheological characterization of shear thickening silica-polyethylene glycol dispersions (of different material configurations in terms of packing fraction, particle size and continuous phase viscosity) to assess their performance and obtain the best STF material configuration for ballistic body armor applications based on the design criteria proposed herein. The ballistic performance assessment results showed that the STFs with high packing fractions which thicken discontinuously, are highly effective compared to the continuously shear thickening fluids. Furthermore, the use of smaller particle size dispersed phase in the STF formulation was determined to be economical. Also, the use of lower molecular weight dispersion medium was suggested as it allows for a broader working temperature range of the STF. Additionally, the technological issues associated with the development and the practical application of STF-Armor were addressed.
Highlights
1 Introduction Shear thickening fluids (STFs) are a class of non-Newtonian fluids, often colloidal dispersions, in which apparent viscosity increases when the shear rate is above a critical value and this flow behavior is dramatic at high particle concentrations called, Discontinuous Shear Thickening (DST)
All the Shear Thickening Fluids (STFs) showed typical concentrated hard sphere dispersion behavior of initial shear thinning followed by shear thickening and subsequent shear thinning
The rheology of pure PEG200 and pure PEG400, carried out as control for the STFs showed slight shear thinning initially and reached newtonian behavior at moderate shear rates but no shear thickening which indicates that the shear thickening phenomenon is caused due to the presence of solid phase and cannot usually occur in pure materials
Summary
Shear thickening fluids (STFs) are a class of non-Newtonian fluids, often colloidal dispersions, in which apparent viscosity increases when the shear rate is above a critical value and this flow behavior is dramatic at high particle concentrations called, Discontinuous Shear Thickening (DST). As the shear thickening develops, the instabilities formed on the free surface (liquid-air interface) eventually cause a portion of the sample between the rheometer plates to be ejected and this loss of sample reduces the torque required to maintain the shear rate, resulting in a decrease in the apparent viscosity (Zone III), but is not a representative of the true STF viscosity [9]. This region does not signify an actual decrease or drop in apparent viscosity, nor does it signify that the fluid has started behaving like a shear thinning fluid. The practical issues associated with the development and the application of STF-Armor were addressed
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