Academic literature on the topic 'Shear thickening fluids'

In this study, we have considered the modal and non-modal stability of fluids with shear-dependent viscosity flowing in a rigid straight pipe. A second order finite-difference code is used for the simulation of pipe flow in the cylindrical coordinate system. The Carreau-Yasuda model where the rheological parameters vary in the range of 0.3 < n < 1.5 and 0.1 < λ < 100 is represents the viscosity of shear- thinning and shear thickening fluids. Variation of the periodic pulsatile forcing is obtained via the ratio Kω/Kο and set between 0.2 and 20. Zero and non-zero streamwise wavenumber have been considered separately in this study. For the axially invariant mode, energy growth maxima occur for unity azimuthal wave number, whereas for the axially non-invariant mode, maximum energy growth can be observed for azimuthal wave number of two for both Newtonian and non-Newtonian fluids. Modal and non-modal analysis for both Newtonian and non-Newtonian fluids show that the flow is asymptotically stable for any configuration and the pulsatile flow is slightly more stable than steady flow. Increasing the maximum velocity for shear-thinning fluids caused by reducing power-low index n is more evident than shear-thickening fluids. Moreover, rheological parameters of Carreau-Yasuda model have ignored the effect on the peak velocity of the oscillatory components. Increasing Reynolds number will enhance the maximum energy growth while a revers behavior is observed by increasing Womersley number.

Improvised Explosive Devices (IEDs) have evolved over the years to become one of the main causes of casualties and fatalities in recent conflicts. One area of research focuses on the improvement of blast attenuation using Shear Thickening Fluid (STF). The 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. Although empirical research and computational models using the non-Newtonian flow characteristics of STF have been conducted to study the effects of STF on blast mitigation, to the author's best knowledge, no specific research has been performed to investigate 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 arrangement, volume concentration of particles, particle size, particle shape, and particle behavior in Newtonian and Non-Newtonian fluid base. The fluid-particle interaction model showed that the arrangement, size, shape and volume concentration of particles had a significant effect on the behavior of STF. Although non-conclusive, the addition of particles in Non-Newtonian fluids showed a promising trend of better shear thickening effect at high shear strain rates.

The absorption of dynamic energy during impact of a material is ubiquitous in industrial, biomedical and military applications. From suspension systems to shock absorbers, the ability to divert or dissipate dynamic energy imposes many challenges in developing these systems. Some typical complex composite fluids, such as shear-thickening fluids (STFs), play a vital role in these challenges. STFs, classified as non-Newtonian fluids, are special fluidic composites of dense suspensions which dramatically change their viscosity when subjected to a change in shear rate or stress. These fluidic composite materials display unusual phase transitions between liquid and “solid” phases, due to recoverable changes in viscosity at a critical rate of shear. In recent years, STFs have stimulated much research interest, in which most studies have been focused on the rheological and energy absorption properties of fabrics soaked with STF under impact. The fundamental knowledge of STFs after their shear-thickening transition is still unarticulated. Without full understanding of the fundamental structure-property relationships of STFs after shear-thickening transition it would not be able to design and optimize a material system with STFs, nor could cost-effective development of STFs as energy-absorbing materials be achieved. The aim of the studies in this thesis is to establish fundamental knowledge in developing STFs as adaptive energy-absorbing materials in practical applications. The studies establish methods and approaches for investigating and characterizing the mechanical as well as the energy-absorbing/dissipation properties of a STF systematically after the shear-thickening transition. The STF adopted in this work was composed of 58 vol.% dispersion of styrene/acrylate particles in ethylene glycol. Microscopic examination was conducted to characterize the size, geometry and distribution of styrene/acrylate particles in the STF, and the rheological behaviours of the STF were measured. Double-cantilever-beam specimens with the STF as adhesive layer were adopted to characterize the mode-I fracture energy of the STF at different crack opening displacement rates, following classic fracture mechanics. High-speed digital video-photography was used to observe the deformation behaviour of the STF. The load-displacement curve as well as the high-speed video recording confirmed that the STF showed a “solid” behaviour at high rates by developing rapid but stable crack extension that corresponded to fracture behaviour. The results indicated that the displacement rate and the STF thickness had a significant effect on the magnitude of the mode-I fracture energy of the STF. The fracture energy increased with an increase in the displacement rate, while a plateau value of about 240 J/m2 was observed at high rates. The measured fracture energy can be used as an effective parameter characterizing the crack resistance or the energy-absorbing capacity of the STF in the solid phase. The lap-shear strength and the braking energy of the STF were quantitatively characterized by a modified single-lap shear test method, performed by using two stainless steel adherends with the STF as adhesive layer. The results indicated that the shear rate had a significant effect on lap shear strength and the braking energy of the STF. Moreover, the studies were conducted to quantitatively characterize the energy absorption capacity of the STF under penetration impact and pull-out fracture at different impact or pull-out speeds. The results confirmed that the penetration rate again had a significant effect on the energy absorbing capacity of the STF. In comparisons with the energy absorbing behaviour of some cellular materials in the literature, the STF outperformed a polyurethane foam in terms of energy absorbing capacity. The ability of a STF to maintain its reversible shear-thickening transition behaviour depends on the integrity and durability of the STF. Cyclic dynamic loading at different magnitudes of durations was applied to the STF in order to quantitatively evaluate its aging behaviour. It was observed that cyclic dynamic loading affected the shear-thickening behaviour of the STF because of deterioration of the styrene/acrylate particles caused by abrasive wear during interaction between them, based on the rheological characterization. This research has delivered some new and original results for solutions to the outstanding problems in developing STFs as energy-absorbing materials. It should bring new opportunities for the development of new and advanced material systems with STFs for practical applications.

Abstract In order to improve the optimisation of mineral processing operations the rheological properties of slurries must be determined as accurately as possible under the conditions that closely resemble actual site conditions. The rheology of particles suspended in Newtonian fluids is well documented. However, the rheology of particles in non-Newtonian fluids has not been the subject of much investigation till now. The work conducted here attempts to fill this gap in knowledge. The rheological properties of slurries are heavily dependent on the solids concentrations and particle-solid interaction. At low solids concentrations, constant viscosity and Newtonian behaviour is observed, but as solids concentration increases the rheological behaviour becomes increasingly complex and non-Newtonian with viscosity becoming dependent on the shear rate. The nature of the non-Newtonian behaviour depends on the solid concentration, particle shape, particle size, particle size distribution and the suspending liquid rheological properties. The suspension/slurry may develop a yield stress and become time dependent in nature as structures develop within the fluid at higher solids concentrations. This study however, is primarily focused on the measurement of the rheological properties, where it is assumed that the fluid will be fully sheared and that the rheological properties will be unlikely to change with time. Shear thickening behaviour of slurries was the focus of this work. The aim was to investigate the slurry concentration region where shear thickening occurs. The first objective of the project was to develop a fluid analogue which will have similar rheological behaviour to that of concentrated tailings from gold mines so that it can be used as a test material to simulate the flow behaviour of the tailings in a pipe. The second objective of this project was to enable the prediction of flow behaviour in the pipe loop under certain conditions using the fluid analogue for slurry from Sunrise dam. In order to achieve the objectives, experiments were carried out to obtain a fluid analogue of a shear thickening slurry. CSL 500 and SR 200 rheometers were used for the characterisation of different fluid analogues and shear thickening mineral slurries. Malvern Sizer, model: mastersizerX v1.1, was used to obtain particle size distributions. A mini pipe loop system, located in the laboratory of the Rheology and Materials Processing Centre (RMPC) was used to get pipe line flow data for comparison with the rheometer data. A few fluid analogues with different suspending medium and different concentrations of glass spheres was tested before finally using, 48 vol% glass spheres in 1.8 wt% CMC solution as a fluid analogue for the mineral tailings obtained from Sunrise dam, WA. For comparison between the pipe line and rheometer data, all pipe line data (in the form of 8V/D) were converted to rheometer data (in the form of du/dr) using the Robinowitsch-Mooney equation. The above comparison indicated that it is possible to produce fluid analogue to simulate the flow behaviour of Sunrise dam slurry using a shear thinning suspending medium with high concentration of glass particles. Shear thickening flow behaviour was clearly observed in the rheometer while it was less predominant in a pipe line flow.

A group of materials that have recently gained a lot of attention in research are shear thickening fluids (STF). A shear thickening fluid (STF) is a material whose viscosity increases significantly when the shear strain rate is at critical value. Most shear thickening fluids are designed by using a colloidal suspension of solid particles in a liquid matrix. This allows solidification of the fluid by congregation of the particles under stress. In this study the experimental findings are focused on assessing the mechanical property of shear thickening fluid (STF) after its transition to a solid phase. On account of determining the shear modulus of STF, bending tests were performed on simply-supported sandwich beam made of double carbon epoxy beams with a STF layer. The stiffness of sandwich beam with STF was evaluated for various midpoint displacements varying from 3 mm to 8 mm at fixed crosshead value of maximum speed 50 mm/s and also at different crosshead values from 10 mm/s to 50 mm/s with a maximum displacement of 8 mm. The numerical value of STF’s shear modulus was calculated by using laminate beam theory. The value obtained for the shear modulus of STF is 0.16 MPa. The experimental result was also compared with FEA by using ANSYS where error is no more than 10%. The special interest is also given to investigate the feasibility of integrating STF into a sandwich cantilever beam with the aim of evaluating the damping capacity and stiffness. The response of shear thickening fluid which is the dispersion of styrene/acrylate particles in ethylene glycol was studied to find critical strain rate at different angular frequency. Experiments are also conducted with a carrier fluid layer between two beams and also two beams glued together with epoxy resin. Considering the boundary conditions, the resonance frequency of the sandwich cantilever beam is obtained from the experiments. The dynamic stiffness of the STF sandwich beam shows better result comparing with the beam with carrier fluid and beams with glued together. As the damping ratio of STF integration with sandwich beam performs better than others, the control of vibration caused by dynamic loading is improved while using STF. Without any external energy source, internal property of shear thickening fluid transforms from liquid phase to a solid phase and absorbs energy caused by vibration.

This thesis aims to study and explore the drop-weight impact-induced solidification process of an STF, consisting of 58 vol% styrene/acrylate particles in ethylene glycol, in a finite volume. The study begins with the characterisation of the mechanical behaviours (i.e., rheological and confined compression behaviours) of the STF. Low-velocity drop-weight impact experiments are conducted to investigate the effect of the STF’s dimensions in a finite volume on the impact behaviour of the STF. It is found that the impact behaviour is related to both the depth and the diameter of the STF. A new model is therefore proposed that the solidification front of an STF advances linearly to the impact velocity with a constant ratio in both the normal and radial directions, respectively, forming a semi-ellipse-like region which is captured by a direct observation with a high-speed camera. When this front propagates to one boundary, a force transmits back to the impact head. The interaction is detected by the load cell and piezoelectric transducers at the boundaries. Moreover, the coupled Eulerian-Lagrangian model and the volume of fluid model are adopted to simulate the development of the solidification front. In both models, the continuous propagation of the solidification front is depicted by expanding of a high-strain-rate region in all directions. The energy absorption under the drop-weight impact is found to decrease with an increase in the depth or width dimension of the STF before their critical dimension is reached due to the extension of the solidification period. Finally, the displacement-control oscillations are conducted on the STF to further explore its reciprocating performance for characterising the resistant force and energy absorption. It is found that the amplitude of displacement has a clear effect on the resistant force and energy absorption, while the frequency has little influence on them after the activation of the shear thickening.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.<br>Includes bibliographical references (leaf 44).<br>The absorption of energy during impacts is ubiquitous in society. From our car seats to body armor, the ability to divert or dissipate unwanted energy is an aspect that has many engineering challenges. One approach to this issue is the use of fluid-filled elastomeric foams. In the present thesis, the fluid within these foams is a non-Newtonian shear-thickening fluid composed of 300 nm silica particles suspended in a solvent, ethylene glycol, at high concentrations, 45-55 %. The field of energy absorption using elastomeric foams has been extensively researched in industry. In addition, the effects and mechanism driving shear-thickening fluids (STF's) has also been well studied in industries involving particle suspensions, such as paints and medical applications. This research intends to combine the analysis of these two systems in an effort to characterize advanced energy absorption mechanism. It was found that the primary factors dominating fluid filled foams containing this STF are the volume fractions and compressional strain rate. In addition, the energy absorption capability of these foams has been compared to that of 'dry' foams and Newtonian-fluid filled foams, and has demonstrated an increase in energy absorption capabilities.<br>by Jose G. Ramirez.<br>S.B.

This thesis aimed to systematically investigate striker shape effect on the mechanical behaviours and energy absorption capabilities of a shear thickening fluid (STF) under low-velocity impact tests. STF is a non-Newtonian colloidal suspension system with a preferable energy absorption capability under both low-velocity and high-velocity impact. This study’s STF consisted of 58.8 vol. % styrene/acrylate co-polymer particles in an ethylene glycol medium. First, rheology tests and scanning electron microscope tests were implemented to study the shear thickening behaviour and submicron-configuration morphology of the styrene/acrylate co-polymer particles, respectively. Subsequently, to investigate the energy absorption properties of this material, low-velocity impact tests were performed by using five types of strikers under various low-impact velocities, with one cone-shaped striker and four cylindrical flat-head strikers with different diameters. The sharp cone-shaped striker was recorded to have lower energy absorption, in comparison with the flat-headed cylindrical striker with the same diameter under all impact velocities. For the cylindrical flat-head strikers, the absorbed energy increased with an increase in the diameter of the striker, although the displacement decreased. These phenomena were attributed to both confinements from the side and bottom boundary towards the STF. In this case, the boundary effect was another factor playing an important role in the low-velocity impact energy absorption, especially with an increase in striker size. In addition, high-speed photography showed cracking in the STF during the impact, indicating the solid-like behaviour of the STF under impact. In this study, energy absorption was assumed to have two stages, before and after the jamming (solidification) zone reached the bottom boundary, which were recognised as the solidification stage and deformation stage, respectively. The impact-activated solidification mechanism indicated that the energy absorption capability depended on the size of the solidification zone. A larger striker is able to produce a larger solidification zone. As the deformation stage in this study, which consisted of an elastic deformation zone and nonlinear deformation zone. For the energy absorption in the deformation stage, using the striker with a cone-shaped head also led to less impact energy absorption in the deformation stage. According to the experimental results, higher impact velocity was able to increase the energy absorption in the deformation stage. In conclusion, the majority of energy absorption occurred in the deformation stage. In other words, an enormous amount of the impact energy was absorbed after the solidification of the STF, rather than during the solidifying process.