Behavior Of Shear Thickening Fluid Research Articles

Contribution of Surface Chemistry to the Shear Thickening of Silica Nanoparticle Suspensions.

Shear thickening is a general process crucial for many processed products ranging from food and personal care to pharmaceuticals. Theoretical calculations and mathematical simulations of hydrodynamic interactions and granular-like contacts have proved that contact forces between suspended particles dominate the rheological characteristic of colloidal suspensions. However, relevant experimental studies are very rare. This study was conducted to reveal the influence of nanoparticle (NP) interactions on the rheological behavior of shear-thickening fluids (STFs) by changing the colloidal surface chemistries. Silica NPs with various surface chemical compositions are fabricated and used to prepare dense suspensions. Rheological experiments are conducted to determine the influence of NP interactions on corresponding dense suspension systems. The results suggest that the surface chemistries of silica NPs determine the rheological behavior of dense suspensions, including shear-thickening behavior, onset stress, critical volume fraction, and jamming volume fraction. This study provides useful reference for designing effective STFs and regulating their characteristics.

Role of Fabric Geometry in Ballistic Performance of Flexible Armour Panels

Energy absorption behavior of flexible armour materials treated with Shear Thickening Fluids (STF) was studied. Five different structures were prepared with varying thread densities of p-aramid yarns, followed by treatment with 60% w/w STF. In untreated condition, plain woven fabrics show highest impact resistance in low velocity impacts, followed by 3/1 twill, 2/2 twill, 5-end satin and 2/2 matt weaves. Ballistic impact mitigation behavior improves with increase in thread density in case of plain woven fabrics. Addition of STF significantly improves both low and high velocity impact behavior of the panels. Low velocity behavior of STF treated fabrics have been published previously [12]. This paper brings together both low and high velocity impact behavior of various geometries of fabrics. It was seen that both primary and secondary yarns are engaged during impact which improves impact mitigation behavior of STF treated fabrics. However, fabrics get jammed at thread densities beyond 32×32 per inch. As was observed earlier in low velocity impact conditions, addition of STF did not enhance performance of fabrics with high thread density in high velocity impact as well.

Stabbing resistance of body armour panels impregnated with shear thickening fluid

This paper presents an investigation on the use of shear thickening fluid (STF) to improve stabbing resistance of soft ballistic body armour. STFs were produced from polyethylene glycol and silica nanoparticles. The effects of silica nanoparticle sizes and silica nanoparticle weight fraction were studied and STFs made with the different compositions were used to impregnate the Twaron® woven fabrics. Systemic investigations into rheological behaviour of STF were carried out experimentally on STFs with different compositions. STF impregnated woven fabric panels were created and tested for stabbing resistance. Stabbing impact tests were conducted on 6 different types of STF impregnated fabric panels against 2 untreated fabric panels, and the results were studied against the benchmark fabrics without STF impregnation. Based on the same number of layers of fabric, the STF impregnation improves the stabbing resistance notably. For same panel areal density, the STF impregnated panels outperform the untreated fabric panel. The results of this research indicate the possibility of lighter ballistic panel materials for higher stabbing protection. It was also found that higher nanoparticle weight fraction and larger nanoparticle size of silica leads to better stabbing resistance performance among the STF impregnated panels.

Study of a shear thickening fluid: the suspensions of monodisperse polystyrene microspheres in polyethylene glycol

ABSTRACTThe monodisperse polystyrene (PS) microspheres were prepared by dispersion polymerization. The rheological properties of shear thickening fluid (STF) based on PS microspheres dispersing in polyethylene glycol with different concentrations were studied through the steady and oscillatory shear at different temperatures, respectively. All suspensions successively present the first shear thinning, the shear thickening, and the second shear thinning. The experimental results indicate that the shear thickening behavior of STF is controlled by the concentration of PS microspheres and temperature, as changed from continuous shear thickening (CST) to discontinuous shear thickening (DST) with increasing solid content or decreasing temperature. The STF is affected by shear rate, temperature, and the viscosity of the dispersed medium, and it is reversible absolutely and presents transient response ability. Both CST and DST behave as dilatancy. The PS microsphere aggregations formed under shear stress may result in the shear thickening in STFs.

The influence of carbon nanotubes on quasi-static puncture resistance and yarn pull-out behavior of shear-thickening fluids (STFs) impregnated woven fabrics

This study focuses on the puncture resistance performance of woven high modulus polypropylene (HMPP) fabric impregnated with shear-thickening fluids (STFs) composed of fumed silica nanoparticles suspended in polyethylene glycol (PEG) and those containing carbon nanotubes (CNTs). The shear-thickening characteristics and rheological features of suspensions were determined at steady and oscillatory shear stress using a stress controlled rheometer. The puncture resistance performance of STF-treated HMPP fabrics were evaluated by the quasi-static puncture test. To gain a better understanding of the effect of these two suspensions on puncture resistance mechanism of fabric, yarn pull-out test was conducted to examine internal shear strength and inter yarn frictional behavior of fabric. The results showed that both the STF-treated fabrics exhibited significant enhancement in puncture resistance performance as compared to neat fabric. However, the fabric impregnated with the suspension containing CNTs showed lower enhancement, due to its lower degree of shear-thickening as confirmed by rheological measurement. The possible improving mechanisms responsible for puncture resistance performance of STF-treated fabrics were also discussed.

Natural convection heat transfer from two vertically aligned circular cylinders in power-law fluids

In this work, laminar natural convection in power-law liquids from a pair of vertically aligned heated cylinders has been studied numerically over the following ranges of conditions: Prandtl number (0.72⩽Pr⩽102), Grashof number (10⩽Gr⩽104), power-law index (0.3⩽n⩽1.5) thereby embracing both shear-thinning and shear-thickening fluid behaviour and the center-to-center gap between the two cylinders was varied over the range (2⩽(S/D)⩽20). The heat transfer characteristics of the lower cylinder are little influenced by the presence of the upper heated cylinder in line with the previous studies. On the other hand, the average Nusselt number for the upper cylinder could be higher or lower than that of the lower cylinder depending upon the value of (S/D), Grashof number and power-law index. Overall, all else being equal, shear-thinning behaviour can enhance heat transfer by up to 100% whereas shear-thickening has adverse influence on the rate of heat transfer. The present results on Nusselt number and drag coefficient have been correlated using simple analytical forms which permit the estimation of these parameters for the two cylinders in a new application with acceptable levels of accuracy. In addition to the overall heat transfer characteristics, the detailed structure of the velocity and temperature fields is visualised in terms of the streamline and isotherm contours over the preceding ranges of parameters.

Momentum and Heat Transfer from a Semi-Circular Cylinder to Power-Law Fluids in the Vortex Shedding Regime

Flow and heat transfer from a semi-circular cylinder to power-law fluids has been studied in the laminar vortex shedding regime for the range of conditions as follows: Reynolds number, 40 ≤ Re ≤ 140; Prandtl number, 0.7 ≤ Pr ≤ 50; and power-law index, 0.2 ≤ n ≤ 1.8. Extensive results are presented in terms of the streamline, vorticity and isotherm profiles, drag and lift coefficients, Strouhal number, and Nusselt number. The influence of Reynolds number, Prandtl number, and power-law index are seen to be more prominent in shear-thinning fluids (n < 1) than that in shear-thickening (n > 1) fluids. The shear-thinning fluid behavior enhances the rate of heat transfer, whereas shear-thickening fluid behavior impedes it.

Natural convection in power-law fluids from two square cylinders in tandem arrangement at moderate Grashof numbers

In this work, free convective flow and heat transfer in power-law fluids from two heated square cylinders in tandem arrangement is studied. The governing differential equations have been solved numerically over wide ranges of Grashof number, 10 ≤ Gr ≤ 1,000, Prandtl number, 0.71 ≤ Pr ≤ 50 and power-law index, 0.4 ≤ n ≤ 1.8. In order to elucidate the extent of inter-cylinder interaction, the non-dimensional inter-cylinder spacing, L/d is varied in the range, 2 ≤ L/d ≤ 6. The results are interpreted in terms of streamline and isotherm contours in the proximity of two cylinders to gain physical insights into the nature of flow. At the next level, the distribution of the local Nusselt number along the surface of the cylinders is presented. At the minimum inter-cylinder spacing due to the intense interference, the downstream cylinder contributes much less to the overall heat transfer whereas it experiences much higher hydrodynamic drag than the upstream cylinder. Broadly, the local and average Nusselt number for both cylinders show a positive dependence on both Grashof and Prandtl numbers. Also, all else being equal, shear-thinning fluid behaviour promotes the rate of heat transfer and shear-thickening fluid behaviour impedes it. Finally, the present numerical results have been correlated by using simple forms of equations thereby enabling the estimation of Nusselt number in a new application.

Numerical study of shear thickening fluid with discrete particles embedded in a base fluid

The Shear Thickening Fluid (STF) is a dilatant material, which displays non-Newtonian characteristics in its unique ability to transit from a low viscosity fluid to a high viscosity fluid. The research performed investigates the STF behavior by modeling and simulation of the interaction between the base flow and embedded rigid particles when subjected to shear stress. The model considered the Lagrangian description of the rigid particles and the Eulerian description of fluid flow. The numerical analysis investigated key parameters such as applied flow acceleration, particle distribution and arrangement, volume concentration of particles, particle size, shape and their behavior in a Newtonian and non-Newtonian fluid base. The fluid-particle interaction model showed that the arrangement, size, shape and volume concentration of the particles had a significant effect on the behavior of the STF. Although non-conclusive, the addition of particles in non-Newtonian fluids showed a promising trend of improved shear thickening effects at high shear strain rates.

Application of shear thickening fluid in ultra high molecular weight polyethylene fabric

AbstractAn advanced stab‐resistant material composed of shear thickening fluid (STF) and ultra high molecular weight polyethylene (UHMWPE) fabric was investigated. STF was prepared by dispersing nanosilica (SiO2) into ethylene glycol. The shear thickening behavior of STF with the increase of the shear rate was observed by PhysicaMCR301. STF/UHMWPE composite fabric was synthesized by impregnating UHMWPE fabric in STF dilution. Stab resistant experiment was conducted on a self‐made stab test machine with knife and spike as stab tool. The results demonstrate that the stab resistant property of the UHMWPE fabric is greatly improved by impregnating STF. The stab resistant property is greatly increased with the increase of mass fraction of silica in STF. Especially, when the mass fraction of SiO2 in STF is 38%, the stab resistance force and energy absorption of STF/UHMWPE are optimal for knife and spike threats. With the same stab resistant properties, the flexibility of UHMWPE fabric impregnated with STF is higher than that of the neat fabric. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Laminar natural convection from a heated square cylinder immersed in power-law liquids

Laminar natural convection heat transfer from a heated long cylinder of square cross-section submerged in stagnant power-law fluids has been investigated numerically. The governing differential equations (continuity, momentum and thermal energy) have been solved over wide ranges of the pertinent dimensionless parameters, namely, Grashof number ( 10 ⩽ Gr ⩽ 10 5 ), Prandtl number ( 0.72 ⩽ Pr ⩽ 100 ) and power-law index ( 0.3 ⩽ n ⩽ 1.8 ) thereby covering both shear-thinning and shear-thickening type fluid behaviours. Detailed structure of the flow is studied in terms of streamline and isotherm patterns while heat transfer characteristics are analyzed in terms of the local Nusselt number distribution over the surface of the cylinder as well as its surface averaged values. Broadly, the flow remains attached to the surface up to larger values of the Grashof number in shear-thinning fluids ( n < 1 ) than that in Newtonian media ( n = 1 ). Similarly, all else being equal, shear-thinning behaviour promotes heat transfer. Indeed, it is possible to enhance the rate of heat transfer by up to 100% under appropriate conditions, i.e., values of the Grashof number, Prandtl number and power-law index. Of course, shear-thickening fluid behaviour has an adverse influence on the rate of heat transfer. In the limiting case of the Newtonian fluid behaviour ( n = 1 ), the present predictions are in excellent agreement with the scant experimental results available in the literature.

Investigation of impact resistance of multilayered woven composite barrier impregnated with the shear thickening fluid

Dynamic properties of the Shear Thickening Fluid (STF) are studied. Two series of tests by the Split Hopkinson Pressure Bar method were carried out to determine the dynamic bulk and shear properties of STF. The hypothesis about the possibility to describe STF behavior by a Newtonian fluid model in the characteristic range of strain rates is confirmed. A simplified mathematical model of the STF is then formulated for the use in computer simulation of ballistic impact tests of multilayered composite protective shells. The effectiveness of the STF impregnation for improvement of ballistic impact characteristics of Kevlar woven fabrics is confirmed. It is concluded that the role of the contact conditions between STF and Kevlar basis in the process of increasing the energy absorption capacity of Kevlar-STF barrier is significant, noting that the mechanism of contact interaction between STF and Kevlar basis can be described by viscous friction law, i.e., the STF behaves almost as a rigid body during the interactions with the solids, while it normally behaves as a fluid. It is also established that the STF impregnation of protective shells with titanium framework not only increases the absorption capacity of the whole package but also reduces the deflection of the metal base.

Two-dimensional unsteady laminar flow of a power law fluid across a square cylinder

The two-dimensional and unsteady free stream flow of power law fluids past a long square cylinder has been investigated numerically in the range of conditions 60 ≤ R e ≤ 160 and 0.5 ≤ n ≤ 2.0 . Over this range of Reynolds numbers, the flow is periodic in time. A semi-explicit finite volume method has been used on a non-uniform collocated grid arrangement to solve the governing equations. The global quantities such as drag coefficients, Strouhal number and the detailed kinematic variables like stream function, vorticity and so on, have been obtained for the above range of conditions. While, over this range of Reynolds number, the flow is known to be periodic in time for Newtonian fluids, a pseudo-periodic flow regime displaying more than one dominant frequency in the lift is observed for shear-thinning fluids. This seems to occur at Reynolds numbers of 120 and 140 for n = 0.5 and 0.6, respectively. Broadly speaking, the smaller the value of the power law index, lower is the Reynolds number of the onset of the pseudo-periodic regime. This work is concerned only with the fully periodic regime and, therefore, the range of Reynolds numbers studied varies with the value of the power law index. Not withstanding this aspect, in particular here, the effects of Reynolds number and of the power law index have been elucidated in the unsteady laminar flow regime. The leading edge separation in shear-thinning fluids produces an increase in drag values with the increasing Reynolds number, while shear-thickening fluid behaviour delays this separation and shows the lowering of the drag coefficient with the Reynolds number. Also, the preliminary results suggest the transition from the steady to unsteady flow conditions to occur at lower Reynolds numbers in shear-thinning fluids than that in Newtonian fluids.

Pre- and post-transition behavior of shear-thickening fluids in oscillating shear

The dynamic shear-thickening behavior of concentrated colloidal suspensions of fumed silica in polypropylene glycol has been investigated. Dynamic frequency sweeps showed that, for any given solids concentration, the complex viscosity at different imposed strain amplitudes followed a unique power-law-type behavior up to the onset of strain thickening. Moreover, similar behavior was also observed in the post-transition state, i.e., the viscosities again superimposed at frequencies beyond the transition frequency. In an attempt to develop a parametric description of this behavior, both the Delaware–Rutgers rule and the concept of a critical shear stress for the onset of shear thickening in steady-state experiments were considered. However, neither approach could account for the observed trends over the entire range of strains and frequency investigated. Plots of the critical shear strains for the onset and the end-point of the transition as a function of frequency were, therefore, used to describe the state of the suspensions for an arbitrary combination of strain and frequency. Finally, Fourier transform (FT) rheology was used to evaluate the extent of non-linearity in the response of the suspensions to dynamic shear, and it was shown that the observed behavior was not significantly influenced by wall slip at the tool–specimen interface.