Rozprawy doktorskie na temat „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.
Includes bibliographical references (leaf 44).
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.
by Jose G. Ramirez.
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.

Cette thèse de doctorat a été financée par l’entreprise SIKA spécialisée dans les matériaux de construction. Les trois chapitres de cette thèse correspondent à la tentative de résolution de trois problématiques d’origine industrielle. Dans le premier chapitre, nous avons étudié l’effet de la concentration en particules sur les propriétés d’écoulement de fluides complexes rhéofluidifiants ou rhéoépaississants et démontré l’origine microscopique de cet effet. Dans le second chapitre, nous avons étudié la floculation de particules colloïdales sous faibles perturbations et mis en évidence l’existence, au cours de la reconstruction, d’un maximum du module élastique. Enfin le troisième chapitre est l’étude d’un diagramme de phase de jet de suspensions concentrées. En régime dilué et semi-dilué, les résultats sont conformes à ceux de la bibliographie, en revanche nous avons étudié un nouveau régime à très haute fraction volumique où le jet, instable, se met à osciller. Nous avons montré que ces oscillations étaient dues au rhéoépaississement de la suspension
This thesis has been done in collaboration with the company SIKA, one of the leader if the construction industry. This thesis report is organized in three chapters where each of them tries to answer a problem coming from industrial processes. In the first chapter, we studied the impact of particles concentration on the flowing properties of complex fluids such as shear-thinning and shear-thickening fluids. We demonstrated the importance of local contacts between particles to explain the evolution of the viscosity with the volume fraction. In the second chapter, we studied the aggregation of colloidal attractive suspensions under small perturbations and proved the existence of a maximum of elastic modulus during the rebuilding of the structure. Finally, the third chapter is a study of a phase diagram of a concentrated suspension jets. In the diluted and semi-diluted regimes, we found results in agreement with the bibliography, meanwhile at very high concentration, we studied a new regime where the jet, unstable, is oscillating. We showed those oscillations can be explained by the shear-thickening behaviour of the suspensions at those high concentrations

Les suspensions de grains rigides dans un fluide constituent une classe de fluides complexes présentant une rhéologie riche. Même dans les cas simples où le fluide est Newtonien, et les grains sphériques, non Browniens et non colloïdaux, les comportements macroscopiques observés restent mal compris, en particulier dans le cas de suspensions concentrées. Dans ces matériaux, la complexité de la dynamique provient de l'équilibre subtil qui se met en place entre les interactions de nature hydrodynamiques portées par le fluide interstitiel et les forces de contact entre les grains. Dans ce travail, nous abordons ces questions sous l'angle de la simulation numérique discrète, dans le cadre du cisaillement simple de suspensions concentrées 2D. Nous modélisons les efforts hydrodynamiques par des interactions de lubrification de paires, couplées à un modèle de contact éventuellement frottant. L'inertie des grains n'est pas négligée. Nous accédons à tous les coefficients du tenseur des contraintes, ce qui permet de mesurer pression, contrainte de cisaillement, et différence des contraintes normales, ainsi que les viscosités associées. L'étude du cisaillement à volume constant nous permet de mettre en évidence l'existence d'une transition de rhéo-épaississement entre un régime visqueuse à bas taux de cisaillement (contrainte proportionnelle au taux de cisaillement) et un régime inertiel à haut taux de cisaillement (contrainte proportionnelle au carré du taux de cisaillement), selon que la contrainte soit dominée par les interactions de lubrification ou par l'inertie des grains. Le taux de cisaillement de transition mesuré est compatible avec un argument d'échelle pour la contrainte, tenant compte de sa divergence avec la fraction volumique. Des simulations du cisaillement à pression constante nous permettent ensuite d'explorer le comportement de suspensions très concentrées (jusqu'à 1% de la fraction volumique de blocage théorique) dans leur domaine d'écoulement visqueux. Nous montrons que la rhéologie du mélange peut se décrire sous la forme d'une loi d'écoulement dépendante du seul nombre visqueux, construit comme le rapport entre un temps caractéristique de réarrangement local des grains sous l'effet des forces visqueuses et un temps typique de convection imposé par l'écoulement. Cette description nous permet de caractériser précisément la divergence de la contrainte avec la concentration en particules. Enfin, nous mesurons la microstructure stationnaire développée dans l'écoulement. Nous mettons en évidence une anisotropie importante des contacts générés, et discutons l'évolution de cette distribution avec la concentration du mélange
Suspensions of rigid grains in a fluid constitute a class of complex fluids that present a rich rheology. Even simpler cases of non-Brownian, non-colloidal spherical grains suspended in a Newtonian fluid feature macroscopic behaviours that are still not completely understood, especially when the concentration of particles is high. In these materials, the complexity of the dynamic is the result of the subtle balance that occurs between hydrodynamic interactions mediated by the interstitial fluid, and contact forces between grains. In this work, we tackle those questions from the point of view of discrete numerical simulations, in the context of the simple shear of 2D concentrated suspensions. Hydrodynamic interactions are modelled by pair lubrication, coupled with a possibly frictional contact law. Grains inertia is not neglected. We have access to the whole stress tensor, allowing the measure of pressure, shear stress, and normal stress difference, as well as their associated viscosities. The study of constant volume simple shear shows the existence of a shear-thickening transition between a viscous regime at low shear rate (stress proportional to the shear rate) and an inertial regime at high shear rate (stress proportional to the shear rate squared), depending on whether the stress is dominated by lubrication interactions or grains inertia. The position of the measured transition shear rate is consistent with a scaling argument for the stress that takes its divergence with concentration into account. Constant pressure simple shear simulations then let us explore the behaviour of very concentrated suspensions (up to 1% to the theoretical jamming fraction) in their viscous flow domain. We show that the rheology of the mix can then be described by a flow law that is only function of the viscous number, constructed as the ratio of a typical time for the local rearrangement of grains subjected to viscous forces, and a convection time consistent with the imposed flow. This allows a precise characterization of the divergence of stress with particles concentration. At last, we measure the stationary microstructure that develops within the flow. We show an important anisotropy of contacts, and discuss the evolution of this distribution with the concentration of the suspension

Cette thèse vise à comprendre l'effet des dynamiques des micelles de copolymères sur leurs propriétés rhéologiques. En effet les copolymères amphiphiles peuvent s'auto-assembler dans l'eau pour former diverses microstructures micellaires sphériques, cylindriques ou lamellaires. Leur dynamique est un paramètre crucial pour définir leur spectre d'applications, en particulier dans le transport de médicaments et dans la synthèse de matériaux méso-structurés. Les micelles se structurent en continu: elles peuvent se former et se dissocier en monomères, se fusionner ou se fragmenter. Nous avons développé une méthode basée sur la fluorescence pour sonder directement les dynamiques micellaires collectives de fusion et de fission dans un bon nombre de copolymères triblocs de la famille PEO-PPO-PEO. Cette thèse se concentre sur l'étude des systèmes micellaires formés par des copolymères triblocs (tensioactifs non ioniques) et les tensioactifs cationiques à des concentrations et des températures où micelles sphériques et micelles cylindriques sont formées. De telles structures peuvent être formées spontanément lorsque le système est soumis à des conditions appropriées de concentration et de température ou à l'induction entre elles en ajoutant des sels inorganiques ou organiques, ou en appliquant des contraintes de cisaillement au système tensioactif/eau.La technique de diffusion de la lumière dynamique (DLS) a été utilisée pour évaluer la transition de la structure dans des solutions micellaires en changeant la température du système et de la structure du système correspondant à des conditions de concentration - température.Des expériences de relaxation de contraintes ont été effectuées où l'assouplissement temporaire de contrainte est mesuré après une déformation instantanée dans des solutions aqueuses de P103. Les temps de relaxation (ou taux) sont comparés avec ceux obtenus par diffusion de la lumière et de leur rapport à la taille des micelles est montré. La relaxation des contraintes présente le comportement de Maxwell. Les temps de relaxation ont montré la dépendance de la température avec des comportements caractéristiques des régimes de micelles sphériques et allongées respectivement.Dans ce travail, nous étudions également le système micellaire CTAnFB avec n la substitution de fluor en positions ortho (F: 2), meta (F: 3) et para (F: 4), à savoir les systèmes CTAortoFB/, CTAmetaFB/eau et CTAparaFB/eau à des concentrations diluées. Nous présentons aussi une étude de la dynamique de la simulation moléculaire de l'hydratation de tensioactifs ortho-, méta- et para-fluorobenzoate et son effet sur la formation de micelles.Nous avons étudié l'effet des contre-ions organiques hydrotropes, 2-, 3- et 4-fluorobenzoïque (2FB-, 3FB- et 4FB-, respectivement) sur le comportement d'épaississement par cisaillement de solutions aqueuses micellaires de micelles en forme de tige de leurs sels avec des cations de cétyltriméthylammonium (CTA2FB, CTA3FB et CTA4FB).Ce travail a contribué à la compréhension de la synergie entre la structure, la dynamique micellaire et la rhéologie dans cette famille de copolymère.

碩士
國防大學中正理工學院
應用化學碩士班
99
Shear thickening fluid (STF) has found its applications in protective materials recently. Generally, the STF consists of colloidal silica particles, their average size being about 450nm, being dispersed in a liquid solvent. However, the particle size of the particles has tremendous influence on the rheological behavior of the suspension. Therefore, in this study, shear thickening behaviors of nano silica , submicron silica and carbon nanotubes dispersions in ethylene glycerol (EG) and polyethylene glycol (PEG) have been studied with rheometer. The dispersion stabilities, thermal characteristics and rheological behaviors of silica suspensions were studied to elucidate the effects of particle size and solid content. This paper also presents an experimental research regarding the ballistic performance of STF-containing Kevlar fabrics and UHDPE. STF shows its potential in many possible civilian applications, such as protective equipment, motorcycle clothing and damping material. The study, shear thickening behaviour and dispersions in room temperature vulcanized (RTV) and Shear thickening fluid have been studied with foam. The dispersion stabilities, thermal characteristics and rheological behaviors of silica suspensions were studied to elucidate the effects of particle size and solid content. This paper also presents an experimental research regarding the impact test performance of STF-RTV composite materials. STF-RTV composite materials shows its potential in many possible civilian applications, such as protective equipment, motorcycle clothing and damping material.

碩士
國立臺北科技大學
化學工程研究所
101
In this study, shear thickening fluid was prepared by two methods. Polyethylene glycol was used as the fluid and silicon dioxide nanoparticles of two different sizes were used as the colloid. From the results, we observed that the mixtures of high loading level of silica nanoparticles with polyethylene glycol demonstrated significant shear thickening behavior. For the PEG fluid containing 40 wt% 15 nm silicon dioxide nanoparticles, the viscosity of fluid instantly increased 29 to 30 times when shear rate increased from 5/s to 28.9/s. Also, for the PEG fluid containing 72.93 wt%, 450 nm silicon dioxide nanoparticles, the viscosity of fluid instantly increased 7 to 9 times when shear rate increased from 61.1/s to 217/s. One of the applications of STF is protection. Impregnating Kevlar fabrics with shear thickening fluid into Kevlar fabric may significantly reduce the layers of Kevlar fabric needed for ballistic impact resistance and improve the flexibility of the composite. In this study, ballistic testing samples were prepared from neat Kevlar fabrics and STF-impregnated ones using Kevlar fabrics with various amount of shear thickening fluid. The result shows that samples reinforced with STF showed a significant improvement in bullet energy absorption.

碩士
國立臺灣科技大學
材料科學與工程系
104
This study reports a “scale up process” of shear thickening fluid (STF). The 40 wt% STF / Kevlar composite was manufactured by two different process. One is impregnating Kevlar fabrics with STF. The other method uses “mangle machine” padding the STF into Kevlar fabrics. The air gun impact test result of the impregnating method showed that STF impregnating with 2 layers Kevlar K129 can significantly increase EDP by 31%. The air gun impact test results of the “mangle machine” method prepared composite is similar with the sample prepared by the impregnating method. However, stab test results showed that sample prepared by the mangle method showed a better resistance than the sample prepared by the impregnating method. The ballistic impact, drop tower, and flexibility tests were conducted. To determine the performance of 30 layers Kevlar without coating STF and the 20 layers STF/Kevlar coated with STF and made by the “mangle machine” method. The result of ballistic impact tests showed both 20 layers STF/Kevlar and 30 layers Kevlar were of the same protection level. They both meet the requirement of NIJ 0101.04-II protection standard. The thickness of 20 layers STF/Kevlar composites were 70% of 30 layers Kevlar. The flexibility tests showed that 20 layers STF/Kevlar composites possesses better flexibility than 30 layers Kevlar. The drop tower test indicated that the 20 layers STF/Kevlar showed similar protective effect as 30 layers Kevlar. The ballistic impact test also showed similar results. Adding STF made the composites lighter and more flexible than conventional Kevlar.

碩士
國立臺北科技大學
化學工程研究所
102
Shear thickening fluid, a type of non-Newtonian fluid, changes viscosity based on shear rate. It has low viscosity at low shear rates, and high viscosity at high shear rates. Thus, this fluid stays mobile under normal conditions, but swiftly hardens upon high-speed impact, resulting in a material useful in liquid armor. So far, most studies have focused on silica-based material as the primary particles in shear thickening fluids, but they often show limited resistance to puncturing. Herein, an approach to synthesize core-shell (alumina/silica) nanoparticles, which can be used as the dispersed phase in the liquid armor materials. Notably, the combination of alumina and silica materials shows significant advantage for enhancing the protective properties of the liquid armor. The core-shell nanoparticles in this study were synthesized using a sol-gel process wherein the silica shell was grown on alumina nanoparticles via a condensation reaction with TEOS. Subsequently, characterization was performed through dynamic light scattering, TEM, and zeta potential measurements. Rheometer measurements were also made using the as-synthesized nanoparticles (treated via sonication) dispersed in a polyethylene glycol medium with varying volume fractions. Thus, the rheological properties of the core-shell system could be investigated and the shear thickening phenomenon observed at high shear rates. Finally, the application of alumina/silica core-shell nanoparticles in liquid armor and the optimization of their comprehensive feasibility and rheological properties are discussed.

碩士
國防大學理工學院
化學工程碩士班
104
Shear thickening fluid (STF) is a colloidal suspension of solid particles suspended in fluid and exhibits the shear thickening phenomenon resulting in large, sometimes discontinuous increase in viscosity above a critical shear rate. This particular rheological property of STFs can be utilized to improve their impact resistance and can be used in many protective applications. However, the impact resistance and threats including puncture, stab and 9 mm bullet impacts (muzzle velocity of 350 ± 10 m/s) varies from the low velocity range to high velocity range. Therefore, the effect of the magnitude of critical shear rate on impact performance is investigated in this research. The critical shear rate of STF is adjusted by varying the size and content of silica particles as well as the solvent composition. In addition, the graphene is also added into STFs to change their rheological property which in turn changing their protective properties. The results of this research can aid in the development of a broad range of protective materials for both consumer and military applications.

碩士
國立臺灣大學
化學工程學研究所
101
Abstract Shear thickening fluid, so called STF, which has a special rheological behavior of the fluid. When suddenly exposed to external shocks, it rapidly presented like a solid which has hardness of properties in a short time (about a few milliseconds). Army Research Laboratory (ARL) first developed shear thickening fluid for military. They researched based on the Kevlar fibers, which was immersed the shear thickening fluid which consists silica nanoparticles and polyethylene glycol mixing, and they called it liquid armor. This shear thickening fluid can greatly enhance the application of Kevlar fiber strength and impact resistance. So far, study of shear thickening fluid based on nano silica particles is now quite mature, the tests on STF-Kevlar fiber containing the liquid armor by spikes, razor, needle, and low-speed bullet attack presented in much effective impact on defense capabilities in general Kevlar fiber. This result makes shear thickening fluid earn greatly in the military''s attention. There are many capable STF research direction currently, so our major research is core-shell (polystyrene / silica) and alumina, which can replace silica nanoparticles as a new dispersed phase and then disperse in polyethylene glycol alcohol. Finally, we use rheometer to test their rheological behavior, exploring the future of this shear thickening fluid.

Title: Flows of incompressible fluids with pressure-dependent viscosity (and their application to modelling the flow in journal bearing) Author: Martin Lanzendörfer Department: Mathematical Institute of Charles University Supervisor: prof. RNDr. Josef Málek, DSc. Abstract: The viscosity of the fluids involved in hydrodynamic lubrication typically depends on pressure and shear rate. The thesis is concerned with steady isothermal flows of such fluds. Generalizing the recent results achieved in the case of homogeneous Dirichlet boundary conditions, the existence and uniqueness of weak solutions subject to the boundary conditions employed in practical applications will be established. The second part is concerned with numerical simulations of the lubrication flow. The experiments indicate that the presented finite element method is successful as long as certain restrictions on the constitutive model are met. Both the restrictions involved in the theoretical results and those indicated by the numerical experiments allow to accurately model real-world lubricants in certain ranges of pressures and shear rates. The last part quantifies those ranges for three representative lubricants. Keywords: existence and uniqueness of weak solutions, finite element method, pressure- thickening, shear-thinning, incompressible fluids,...

Advanced impact protection systems can experience serious damage due to contact with projectiles such as fragments or entire fan blades. To prevent catastrophic damage of such systems will require sophisticated materials and complex designs. The development of advanced ballistic protection systems will place increased emphasis on the use of composite materials and on numerical simulations to assess these new systems due to the cost and limitations of testing facilities and the increased capability of computing power. Example applications include the design of body armor for the protection of personnel, the design of fragment containment systems for aircraft engines, and the design of orbital debris shielding for the protection of manned spacecraft. The current research has developed a new mesomechanical particle-element material model for woven material impact response, a velocity dependent friction model to simulate yarn interactions, and a strain rate dependent model for Kevlar. In recent research, a new class of shear-thickening fluid (STF) composites has been developed for use in impact protection systems. Advancements in the current work include a Bingham shear stress model for STF effects and a new mixture equation of state for the STF Kevlar that captures the thermodynamic properties of the constituents. The numerical methods and material model developed in this research have been validated through the simulation of three dimensional impact experiments on different Kevlar target geometries. This dissertation also provides new data for fragment simulating projectile impacts on Kevlar with different boundary conditions and new data for aluminum cylinder and steel disk projectile impacts on neat and STF Kevlar with different boundary conditions.
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碩士
逢甲大學
纖維與複合材料學系
105
In order to reduce the number of layers of Kevlar fabric effectively and to improve the mobility of personnel, we used colloidal silica dispersed in polyethylene glycol to prepare shear thickening fluid that was used in protective armor with effective protective properties. The addition of graphene oxide was discussed in this paper to investigate its impact on the effect of shear fluid properties. In this study, we investigated the puncture test, falling weight impact test, rheological test and torsion test of colloidal silica in different molecular weight of polyethylene glycol (PEG) impregnated Kevlar KK10 fabric. The falling weight impact test was carried out by using blunt-nosed bullet (9 mm) and pointed bullet (7.62 mm), and hope the test results can be applied to the anti-bullet protection. The experimental results showed that the fabric impregnated with PEG molecular weight of 200 and 60 wt% of colloidal silica had better puncture resistance than that of non-impregnated fabric by 414%. In the falling weight impact test with blunt-nosed bullet, the absorption energy of the impregnated fabric was increased by 66.87%; whereas the absorption energy of the impregnated fabric with pointed bullet was increased by 126.11%. The addition of graphene oxide impacted on the shear thickening phenomenon, and enhanced the anti-puncture property of PEG with molecule weight of 600; however, it decreased that of PEG with molecule weight of 200.