194 research outputs found

    A state-of-the-art review on magnetorheological elastomer devices

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    ยฉ 2014 IOP Publishing Ltd. During the last few decades, magnetorheological (MR) elastomers have attracted a significant amount of attention for their enormous potential in engineering applications. Because they are a solid counterpart to MR fluids, MR elastomers exhibit a unique field-dependent material property when exposed to a magnetic field, and they overcome major issues faced in magnetorheological fluids, e.g. the deposition of iron particles, sealing problems and environmental contamination. Such advantages offer great potential for designing intelligent devices to be used in various engineering fields, especially in fields that involve vibration reduction and isolation. This paper presents a state of the art review on the recent progress of MR elastomer technology, with special emphasis on the research and development of MR elastomer devices and their applications. To keep the integrity of the knowledge, this review includes a brief introduction of MR elastomer materials and follows with a discussion of critical issues involved in designing magnetorheological elastomer devices, i.e. operation modes, coil placements and principle fundamentals. A comprehensive review has been presented on the research and development of MR elastomer devices, including vibration absorbers, vibration isolators, base isolators, sensing devices, and so on. A summary of the research on the modeling mechanical behavior for both the material and the devices is presented. Finally, the challenges and the potential facing magnetorheological elastomer technology are discussed, and suggestions have been made based on the authors' knowledge and experience

    Development of Rotary Variable Damping and Stiffness Magnetorheological Dampers and their Applications on Robotic Arms and Seat Suspensions

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    This thesis successfully expanded the idea of variable damping and stiffness (VSVD) from linear magnetorheological dampers (MR) to rotary magnetorheological dampers; and explored the applications of rotary MR dampers on the robotic arms and seat suspension. The idea of variable damping and stiffness has been proved to be able to reduce vibration to a large degree. Variable damping can reduce the vibration amplitude and variable stiffness can shift the natural frequency of the system from excitation and prevent resonance. Linear MR dampers with the capacity of variable damping and stiffness have been studied by researchers. However, Linear MR dampers usually require larger installation space than rotary MR dampers, and need more expensive MR fluids to fill in their chambers. Furthermore, rotary MR dampers are inherently more suitable than linear MR dampers in rotary motions like braking devices or robot joints. Hence, rotary MR dampers capable of simultaneously varying the damping and stiffness are very attractive to solve angular vibration problems. Out of this motivation, a rotary VSVD MR damper was designed, prototyped, with its feature of variable damping and stiffness verified by experimental property tests in this thesis. Its mathematical model was also built with the parameters identified. The experimental tests indicated that it has a 141.6% damping variation and 618.1% stiffness variation. This damperโ€™s successful development paved the way for the applications of rotary MR dampers with the similar capability of variable damping and stiffness

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    ํ•™์œ„๋…ผ๋ฌธ (๋ฐ•์‚ฌ) -- ์„œ์šธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› : ๊ณต๊ณผ๋Œ€ํ•™ ์žฌ๋ฃŒ๊ณตํ•™๋ถ€, 2020. 8. ์„œ์šฉ์„.Magnetorheological (MR) fluids are typically consist of magnetic particles (Carbonyl Iron, Fe2O3, Fe3O4 and so on) in a magnetically insulating fluid (water, silicon oil and so on). When a magnetic field induces attractive interactions between the magnetic particles, these particles form a solid-like network of fibril shapes within a few milliseconds oriented along the direction of the magnetic field. Reverse transition occurs as soon as the magnetic field is switched off. These features lead to remarkable changes in the rheological properties of the fluid which shows wide potential applications such as dampers, brakes, shock observers, drug delivery, and robotics, etc and could be controlled by adjusting the strength of the magnetic field depending on applications. Despite substantial advanced in commercialization, MR fluids have long-term stability issues that significantly limit their usefulness and also need to be predicted the precise flow behavior. In this thesis, we propose the constitutive equation to predict the flow behavior of MR fluid and investigate a number of MR fluid composed of soft-magnetic composite particles to overcome the sedimentation drawback. Firstly, as modeling and analysis are essential to optimize material design, describe the flow behavior over a wide range of shear rate and distinguish between static yield stress and dynamic yield stress, the precise knowledge of the relationships between the suspension rheological properties and such variables as the deformation rate, the applied magnetic field strength, and the composition are required. So we re-analyze the constitutive equation proposed before to describe the MR fluids flow and propose new constitutive equation. The proposed Seo-Seo model predicted the flow behavior precisely compared to pre-exist constitutive model and also yielded a quantitatively and qualitatively precise description of MR fluid rheological behavior based on relatively few experimental measurements. To overcome sedimentation drawback, the core/shell structured Foamed polystyrene/Fe3O4 Particles were synthesized by applying a dual-step processing comprising pickering emulsion polymerization, subsequently by the foaming of polystyrene core using the supercritical carbon dioxide fluid foaming process. Through these processes, the density of composite was dropped significantly and the long-term stability was improved. As polystyrene located core part and magnetic particle contact directly, the magnetorheological properties of the Foamed polystyrene/Fe3O4 were considerable compared to pure Fe3O4. Even though the core/shell structured Foamed polystyrene/Fe3O4 showed considerable level, the magnetorheological properties got worsen because polystyrene is magnetically non-active. So, we synthesized hollow shape Fe3O4 particles without any magnetically non-active template. As a result, compared to the core/shell structured Foamed polystyrene/Fe3O4, the density of hollow shape Fe3O4 particles rise slightly and the magnetorheological properties reached outstanding level, and the long-term stability maintained. Also, the conformation of solid-like network of fibril shapes changes were investigated by using micro/nano size Fe3O4 particles to verify the reinforcement effect. As the particle size increases, the magnetorheological properties improve due to a rise of the magnetic saturation level. However, depending on the ratio of the nano size Fe3O4 particles, an overturning of the magnetorheological properties and the magnetic saturation was observed. This phenomenon is because of the cavity among the micro size Fe3O4 particles. The micro size Fe3O4 particles develops a relatively coarse solid-like network of fibril shapes. The chain conformation of a bidisperse MR fluid shows quite different from that of the micron size Fe3O4 particles-based fluids. The nano size Fe3O4 particles appear to fill in the cavity among the micro size Fe3O4 particles. As a result, this distinct conformation reinforced the magnetorheological properties. Finally, the shape effect of the magnetic particle on magnetorheological properties and sedimentation stability was investigated by using two types of sendust which are bulk and flake type. The flake type sendust has a small demagnetization factor because its domain orients one direction. This feature lead to extraordinary behavior which is a rapid transition to solid-like network at low magnetic field. Also, its high aspect ratio leads to a large drag coefficient which improve the long-term stability.์ž๊ธฐ์œ ๋ณ€์œ ์ฒด๋Š” ๋ฌผ ๋˜๋Š” ๋น„์ˆ˜๊ณ„(์‹ค๋ฆฌ์ฝ˜ ์˜ค์ผ ๋“ฑ)์˜ ์œ ์ฒด์— ์žํ™” ๊ฐ€๋Šฅํ•œ ๋ฏธ์„ธ์ž…์ž(์ฒ  ๋งˆ์ดํฌ๋กœ ์ž…์ž)๋ฅผ ๋ถ„์‚ฐ์‹œํ‚จ ํ˜„ํƒ์•ก์œผ๋กœ์„œ, ์™ธ๋ถ€๋กœ๋ถ€ํ„ฐ ์ œ๊ณต๋˜๋Š” ๊ฐ•ํ•œ ์ž๊ธฐ์žฅ์— ๋”ฐ๋ผ ์งง์€ ์‹œ๊ฐ„์•ˆ์— ํƒ„์„ฑ, ์†Œ์„ฑ, ์ ๋„ ๊ฐ™์€ ์ž๊ธฐ์œ ๋ณ€ํšจ๊ณผ๋ฅผ ๋‚˜ํƒ€๋‚ด๋Š” ์œ ์ฒด๋ฅผ ๋งํ•œ๋‹ค. ์ž๊ธฐ์œ ๋ณ€์œ ์ฒด๋Š” ์™ธ๋ถ€ ์ž๊ธฐ์žฅ์— ์˜ํ•ด ์œ ๋ณ€ํšจ๊ณผ๋ฅผ ์กฐ์ ˆํ•  ์ˆ˜ ์žˆ๊ธฐ ๋•Œ๋ฌธ์— ๋‹ค์–‘ํ•œ ์‘์šฉ๋ถ„์•ผ๋กœ์˜ ์ ์šฉ ๊ฐ€๋Šฅ์„ฑ์— ๋Œ€ํ•œ ๊ด€์‹ฌ์ด ์ฆ๊ฐ€ํ•˜๊ณ  ์žˆ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ์ž์„ฑ์ž…์ž์™€ ํ˜„ํƒ ์œ ์ฒด์™€์˜ ๋ฐ€๋„ ์ฐจ์— ์˜ํ•ด ๋ฐœ์ƒํ•˜๋Š” ์นจ์ „ํ˜„์ƒ์œผ๋กœ ์ธํ•ด ์ž๊ธฐ์œ ๋ณ€์œ ์ฒด์˜ ์‹ค์ œ์ ์ธ ์‘์šฉ์ด ์ œํ•œ๋˜๊ณ  ์žˆ๋‹ค. ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ์ž๊ธฐ์œ ๋ณ€์œ ์ฒด์˜ ๊ฑฐ๋™์„ ์˜ˆ์ธกํ•˜๋Š” ๊ตฌ์„ฑ๋ฐฉ์ •์‹์„ ์ œ์•ˆํ•˜๊ณ , ์นจ์ „ ๋ฌธ์ œ๋ฅผ ๊ทน๋ณตํ•˜๊ธฐ ์œ„ํ•ด ์—ฐ์ž์„ฑ ๋ณตํ•ฉ์ฒด๋กœ ๊ตฌ์„ฑ๋œ ์ž๊ธฐ์œ ๋ณ€์œ ์ฒด๋ฅผ ์กฐ์‚ฌํ•œ๋‹ค. ์žฌ๋ฃŒ ์„ค๊ณ„๋ฅผ ์ตœ์ ํ™”ํ•˜๊ธฐ ์œ„ํ•ด ํ•„์ˆ˜์ ์œผ๋กœ ๊ด‘๋ฒ”์œ„ํ•œ ์ „๋‹จ ์†๋„์— ๊ฑธ์นœ ํ๋ฆ„ ๋™์ž‘์„ ์„ค๋ช…ํ•˜๊ณ  ์ •์  ํ•ญ๋ณต ์‘๋ ฅ๊ณผ ๋™์  ํ•ญ๋ณต ์‘๋ ฅ์„ ๊ตฌ๋ถ„ํ•˜์—ฌ์•ผ ํ•œ๋‹ค. ๋˜ํ•œ, ํ˜„ํƒ์•ก์˜ ์œ ์ „ํ•™์  ํŠน์„ฑ๊ณผ ๋ณ€ํ˜•๋ฅ , ์ ์šฉ๋œ ์ž๊ธฐ์žฅ ๊ฐ•๋„ ๋ฐ ๊ตฌ์„ฑ๊ณผ ๊ฐ™์€ ๋ณ€์ˆ˜ ์‚ฌ์ด์˜ ๊ด€๊ณ„์— ๋Œ€ํ•œ ์ •ํ™•ํ•œ ์ง€์‹์ด ํ•„์š”ํ•˜๋‹ค. ๋”ฐ๋ผ์„œ, ์ž๊ธฐ์œ ๋ณ€์œ ์ฒด์˜ ํ๋ฆ„์„ ์„ค๋ช…ํ•˜๊ธฐ ์œ„ํ•œ ๊ธฐ์กด์˜ ์ œ์•ˆ๋œ ๊ตฌ์„ฑ๋ฐฉ์ •์‹์„ ๋ถ„์„ํ•˜๊ณ  ์ƒˆ๋กœ์šด ๊ตฌ์„ฑ๋ฐฉ์ •์‹์„ ์ œ์•ˆํ•œ๋‹ค. ์ƒˆ๋กญ๊ฒŒ ์ œ์•ˆํ•œ ๊ตฌ์„ฑ ๋ฐฉ์ •์‹์ธ ์„œ-์„œ ๋ชจ๋ธ์€ ๊ธฐ์กด์— ์กด์žฌํ•˜๋Š” ๊ตฌ์„ฑ๋ฐฉ์ •์‹๊ณผ ๋น„๊ตํ•˜์—ฌ ์œ ์ฒด์˜ ํ๋ฆ„์„ ์ •ํ™•ํ•˜๊ฒŒ ์˜ˆ์ธกํ•˜์˜€๊ณ , ๋น„๊ต์  ์ ์€ ์‹คํ—˜ ๊ฐ’์„ ๋ฐ”ํƒ•์œผ๋กœ ์ž๊ธฐ์œ ๋ณ€์œ ์ฒด์˜ ํ๋ฆ„์— ๋Œ€ํ•œ ์ •๋Ÿ‰์ , ์งˆ์ ์œผ๋กœ ์ •๋ฐ€ํ•œ ์„ค๋ช…์„ ๋„์ถœํ•˜์˜€๋‹ค. ์นจ์ „ ๋ฌธ์ œ๋ฅผ ๊ทน๋ณตํ•˜๊ธฐ ์œ„ํ•ด ํ”ผ์ปค๋ง ์—๋ฉ€์ „ ์ค‘ํ•ฉ์„ ๋ฐ ์ดˆ์ž„๊ณ„ ์ด์‚ฐํ™”ํƒ„์†Œ๋ฅผ ์ด์šฉํ•œ ๋ฐœํฌ๊ณต์ •์˜ ์ด์ค‘ ๊ณต์ • ์ฒ˜๋ฆฌ๋ฅผ ํ†ตํ•ด ์ฝ”์–ด-์‰˜ ๊ตฌ์กฐ์˜ ๋ฐœํฌ ์Šคํƒ€์ด๋ Œ ๊ณ ๋ถ„์ž-์ฒ  ๋ณตํ•ฉ์ฒด๋ฅผ ํ•ฉ์„ฑํ•˜์˜€๋‹ค. ์ด์ค‘ ๊ณต์ • ์ฒ˜๋ฆฌ๋ฅผ ํ†ตํ•ด ๋ณตํ•ฉ์ฒด์˜ ๋ฐ€๋„๊ฐ€ ํ˜„์ €ํžˆ ๋–จ์–ด์ง€๊ณ  ์žฅ๊ธฐ ์•ˆ์ •์„ฑ์ด ํ–ฅ์ƒ๋˜์—ˆ๋‹ค. ๋˜ํ•œ, ์Šคํƒ€์ด๋ Œ์ด ์ฝ”์–ด ๋ถ€๋ถ„์— ์œ„์น˜ํ•˜์—ฌ, ์ฒ  ์ž…์ž๊ฐ€ ์ง์ ‘์ ์ธ ์ ‘์ด‰์„ ํ†ตํ•ด ๋†’์€ ์ž๋ ฅ ํŠน์„ฑ์„ ์–ป์—ˆ๋‹ค. ์ฝ”์–ด-์‰˜ ๊ตฌ์กฐ์˜ ๋ฐœํฌ ์Šคํƒ€์ด๋ Œ ๊ณ ๋ถ„์ž-์ฒ  ๋ณตํ•ฉ์ฒด์˜ ์ž๋ ฅ ํŠน์„ฑ์ด ์ƒ๋‹นํ•œ ์ˆ˜์ค€์„ ๋ณด์˜€์Œ์—๋„ ๋ถˆ๊ตฌํ•˜๊ณ , ์Šคํƒ€์ด๋ Œ์ด ์ž๋ ฅ์ ์œผ๋กœ ๋น„ํ™œ์„ฑํ™” ๋ฌผ์งˆ์ด๋ฏ€๋กœ ์ˆœ์ˆ˜ํ•œ ์ฒ ์— ๋น„ํ•ด ์ž๋ ฅ ํŠน์„ฑ์€ ์•ฝํ™”๋˜์—ˆ๋‹ค. ๋”ฐ๋ผ์„œ ์ž๋ ฅ์ ์œผ๋กœ ๋น„ํ™œ์„ฑํ™” ๋ฌผ์งˆ์ธ ์Šคํƒ€์ด๋ Œ์„ ์ œ๊ฑฐํ•˜์—ฌ ์ง€์ง€๋Œ€๊ฐ€ ์—†๋Š” ์ค‘๊ณตํ˜•์ƒ์˜ ์ฒ  ์ž…์ž๋ฅผ ํ•ฉ์„ฑํ•˜์˜€๋‹ค. ๊ทธ ๊ฒฐ๊ณผ, ์ฝ”์–ด-์‰˜ ๊ตฌ์กฐ์˜ ๋ฐœํฌ ์Šคํƒ€์ด๋ Œ ๊ณ ๋ถ„์ž-์ฒ  ๋ณตํ•ฉ์ฒด์— ๋น„ํ•ด ์ค‘๊ณตํ˜•์ƒ์˜ ์ฒ  ์ž…์ž๋Š” ๋ฐ€๋„๊ฐ€ ์•ฝ๊ฐ„ ์ƒ์Šนํ•˜์˜€์œผ๋‚˜ ๋†’์€ ์ž๋ ฅํŠน์„ฑ์„ ๋ณด์˜€๊ณ  ์žฅ๊ธฐ ์•ˆ์ •์„ฑ์ด ์œ ์ง€๋˜์—ˆ๋‹ค. ์ถ”๊ฐ€์ ์œผ๋กœ ๋งˆ์ดํฌ๋กœ/๋‚˜๋…ธ ํฌ๊ธฐ์˜ ์ฒ  ์ž…์ž๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ํ”ผ๋ธŒ๋ฆด ๊ตฌ์กฐ์˜ ๋ณด๊ฐ•ํšจ๊ณผ๋ฅผ ๊ฒ€์ฆํ•˜์˜€๋‹ค. ์ž…์ž ํฌ๊ธฐ๊ฐ€ ์ฆ๊ฐ€ํ•จ์— ๋”ฐ๋ผ ์ž๊ธฐ ํฌํ™” ์ˆ˜์ค€์˜ ์ƒ์Šน์œผ๋กœ ์ž๋ ฅํŠน์„ฑ์ด ๊ฐœ์„ ๋˜์—ˆ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜, ๋‚˜๋…ธ ํฌ๊ธฐ์˜ ์ฒ  ์ž…์ž์˜ ๋น„์œจ์— ๋”ฐ๋ผ ์ž๋ ฅํŠน์„ฑ๊ณผ ์ž๊ธฐ ํฌํ™” ํ˜„์ƒ์˜ ์—ญ์ „ํ˜„์ƒ์ด ๊ด€์ฐฐ๋˜์—ˆ๋‹ค. ์ด ํ˜„์ƒ์€ ๋งˆ์ดํฌ๋กœ ํฌ๊ธฐ์˜ ์ฒ  ์ž…์ž์˜ ํ”ผ๋ธŒ๋ฆด ๊ตฌ์กฐ๋ฅผ ํ˜•์„ฑ์‹œ์— ์ฒ  ์ž…์ž ์‚ฌ์ด์˜ ๊ณต๋™๋•Œ๋ฌธ์ด๋‹ค. ๋งˆ์ดํฌ๋กœ ํฌ๊ธฐ์˜ ์ฒ  ์ž…์ž๋Š” ๋น„๊ต์  ๊ฑฐ์นœ ํ”ผ๋ธŒ๋ฆด ๊ตฌ์กฐ๋ฅผ ํ˜•์„ฑํ•œ๋‹ค. ํ˜ผ์„ฑ ์ž๊ธฐ์œ ๋ณ€์ฒด๋Š” ๋งˆ์ดํฌ๋กœ ํฌ๊ธฐ์˜ ์ฒ  ์ž…์ž์™€๋Š” ๋‹ค๋ฅธ ํ”ผ๋ธŒ๋ฆด ๊ตฌ์กฐ๋ฅผ ํ˜•์„ฑํ•œ๋‹ค. ๋‚˜๋…ธ ํฌ๊ธฐ์˜ ์ฒ  ์ž…์ž๋“ค์ด ๋งˆ์ดํฌ๋กœ ํฌ๊ธฐ์˜ ์ฒ  ์ž…์ž ์‚ฌ์ด์˜ ๊ณต๋™์„ ์ฑ„์›€์œผ๋กœ ์ธํ•ด์„œ ์ž๋ ฅํŠน์„ฑ์ด ํ–ฅ์ƒ๋˜์—ˆ๋‹ค. ๋งˆ์ง€๋ง‰์œผ๋กœ, ๋ฒŒํฌํ˜•๊ณผ ๋ฐ•๋ฆฌํ˜•์˜ ์„ผ๋”์ŠคํŠธ๋ฅผ ์ด์šฉํ•˜์—ฌ ์ž๊ธฐ์ž…์ž์˜ ๋ชจ์–‘์ด ์œ ๋ณ€์  ํŠน์„ฑ์— ๋ผ์น˜๋Š” ์˜ํ–ฅ์„ ์กฐ์‚ฌํ•˜์˜€๋‹ค. ๋ฐ•๋ฆฌํ˜• ์„ผ๋”์ŠคํŠธ์˜ ์ž๊ตฌ๋Š” ํ•œ ๋ฐฉํ–ฅ์œผ๋กœ ์ •๋ ฌ๋˜์–ด ์žˆ์–ด ์ž‘์€ ๊ฐ์ž์œจ์„ ๊ฐ–๊ณ , ์ด ํŠน์ง•์€ ์ €์ž๊ธฐ์žฅ์—์„œ ํ”ผ๋ธŒ๋ฆด ๊ตฌ์กฐ๋กœ์˜ ๋น ๋ฅธ ์ „ํ™˜์„ ๊ฐ€๋Šฅํ•˜๊ฒŒ ํ•œ๋‹ค. ๋˜ํ•œ, ๋ฐ•๋ฆฌํ˜• ์„ผ๋”์ŠคํŠธ์˜ ๋†’์€ ์ข…ํšก๋น„๋กœ ์ธํ•œ ํ•ญ๋ ฅ๊ณ„์ˆ˜๋Š” ์žฅ๊ธฐ ์•ˆ์ •์„ฑ์„ ํ–ฅ์ƒ์‹œ์ผฐ๋‹ค.Chapter 1. Introduction and Background . 0 1.1. Magnetorheological (MR) Fluids 0 1.2. Applications of MR fluids . 2 1.3. Rheology 2 1.3.1. Flow behavior . 3 1.3.1.1. Definition of terms 3 1.3.1.1.1. Shear stress 5 1.3.1.1.2. Shear rate 5 1.3.1.1.3. Shear viscosity . 5 1.3.1.2. Flow and viscosity curve 7 1.3.1.2.1. Ideal viscous flow. 7 1.3.1.2.2. Shear-thinning flow and Shear-thickening . 9 1.3.1.2.3. Yield stress 9 1.3.2. Viscoelastic behavior 11 1.3.2.1. Storage modulus and Loss modulus . 11 Reference 12 Chapter 2. Constitutive Equation . 14 2.1. Introduction . 14 2.2. Rheological Models for the Yield Stress . 18 2.2.1. Static Yield Stress versus Dynamic Yield Stress . 18 2.2.2. Yield Stress Dependency on the Magnetic Field Strength 22 2.2.3. Mechanism of Structure Evolution . 24 2.3. Conclusion . 26 Reference . 27 Chapter 3. High-Performance Magnetorheological Suspensions of Pickering Emulsion Polymerized Polystyrene/Fe3O4 Particles with Enhanced Stability 31 3.1. Introduction 31 3.2. Experimental Section 33 3.2.1. Synthesis of Polystyrene/Fe3O4 particles . 33 3.2.2. Synthesis of Foamed Polystyrene/Fe3O4 particles 34 3.2.3. Characterization 37 3.3. Results and Discussion 41 3.3.1 Morphology . 41 3.3.2. Magnetorheological Behaviors . 42 3.3.3. Yield Stress of the MR Fluids 47 3.3.4. Structure Evolution Mechanism and the Suspension Stability . 54 3.4. Conclusion . 59 References . 61 Chapter 4. Template Free Hollow Shaped Fe3O4 Micro-Particles for Magnetorheological Fluid . 65 4.1 Introduction . 65 4.2. Experiment Section . 67 4.2.1. Synthesis of Fe3O4 particles (Pure Fe3O4) . 67 4.2.2. Synthesis of PS/Fe3O4 particles (Picker) . 68 4.2.3. Synthesis of PS/Fe3O4@Fe3O4 particles (C-picker) 68 4.2.4. Synthesis of templet free hollow shaped Fe3O4 (H-Picker) . 69 4.2.5. Characterization 69 4.3. Results and Discussion . 70 4.3.1. Particle Morphologies and Magnetic Hysteresis Curve 70 4.3.2. Magnetorheological Behaviors . 76 4.3.3. Yield Stress of the MR Fluids . 80 4.3.4. Mechanism of Structure Evolution and Suspension Stability . 84 4.4. Conclusion 89 Reference 90 Chapter 5. Bidisperse MR Fluids Using Nano/micro Size Fe3O4 particles . 95 5.1. Introduction 95 5.2. Experiment Section 99 5.2.1. Material. 99 5.2.2. Characterization Methods . 99 5.3. Results and Discussion . 99 5.4. Conclusion 106 References . 107 Chapter 6. Shape effect of magnetic particle on magnetorheological (MR) properties and sedimentation stability 108 6.1. Introduction . 108 6.2. Experiment Section . 109 6.2.1. Material . 109 6.2.2. Characterization Methods 109 6.3. Results and Discussion 110 6.3.1. Particle Morphologies and Magnetic Hysteresis Curve . 110 6.3.2. Magnetorheological Behaviors 116 6.3.3. Yield Stress of the MR Fluids . 120 6.3.4. Mechanism of Structure Evolution and Suspension Stability . 124 6.4. Conclusion . 129 References 130 Chapter 7. Conclusions 135 ๊ตญ๋ฌธ์ดˆ๋ก 139 List of Publication 141 Appendix . 142 Appendix A. Improvement of Mechanical Properties by Introducing Curable Functional Monomers in Stereolithography 3D PrintingDocto

    Magnetic Hybrid-Materials

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    Externally tunable properties allow for new applications of suspensions of micro- and nanoparticles in sensors and actuators in technical and medical applications. By means of easy to generate and control magnetic fields, fluids inside of matrices are studied. This monnograph delivers the latest insigths into multi-scale modelling, manufacturing and application of those magnetic hybrid materials

    Rheological and stability properties of magnetorheological fluid with superparamagnetic maghemite nanoparticles

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    This research is focused on the development of a new magnetorheological (MR) fluid which contains maghemite (ฮณ-Fe2O3) nanoparticles so as to improve its performance. The performance of MR fluid is presented in terms of physical and rheological properties and its application in MR device. In this work, the ฮณ-Fe2O3 has been synthesized using co-precipitation method and coated with oleic acid. Two types of MR fluids were prepared, bidisperse MR fluid containing carbonyl iron (CI) microparticles substituted with ฮณ-Fe2O3 and MR fluid utilizing ฮณ-Fe2O3 additive. MR fluid containing ฮณ-Fe2O3 showed great improvement exhibiting reduced sedimentation rate and enhanced re-dispersibility. During the period of 50 hours, the bidisperse MR fluid with 5 wt% of ฮณ-Fe2O3 reduced 15% of sedimentation rate and MR fluid with 1 wt% of ฮณ-Fe2O3 additive reduced 9.6% of sedimentation rate compared to pure CI MR fluid. The rheological properties of the MR fluid were analyzed with respect to the rheological models of Bingham Plastic, Herschel Bulkley and Casson models. The rheological properties of bidisperse MR fluid revealed that the substitution of 5 wt% ฮณ-Fe2O3 increased the yield stress by 8.5% but further substitution of ฮณ-Fe2O3 would slightly decrease the yield stress. On the other hand, the MR fluid added with ฮณ-Fe2O3 additive showed improvement in yield stress over the entire range of magnetic field applied. The results indicated that the addition of 1 wt% of ฮณ-Fe2O3 in MR fluid increased the yield stress by 11.7%. The performance of MR fluid using MR valve equipped with a hydraulic bypass damper resulted in improvement of damping force when ฮณ-Fe2O3 is added. The MR fluid with 1 wt% ฮณ-Fe2O3 additive improved the maximum damping force up to 11.1% compared to the pure MR fluid. Therefore, the substitution and addition of ฮณ-Fe2O3 nanoparticles in the MR fluid improved both its physical and rheological properties, hence it can potentially be used in commercial application as a simple and reliable damping device

    Study of failure symptoms of a single-tube MR damper using an FEA-CFD approach

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    From SAGE Publishing via Jisc Publications RouterHistory: epub 2020-11-03Publication status: PublishedA new magnetorheological (MR) damper has been designed, manufactured, modelled and tested under cyclic loads. A faulty behaviour of the damper was accidentally detected during the experiments. It was deduced that the presence of air bubbles within the MR fluid is the main reason for that failure mode of the damper. The AMT-Smartec+ MR fluid used in the current study, a new MR fluid whose characteristics are not available in the literature, exhibits good magnetic properties. However, the fluid has a very high viscosity in the absence of magnetic field. It is assumed that this high viscosity enables the retention of air bubbles in the damper and causes the faulty behaviour. To prove this assumption, a coupled numerical approach has been developed. The approach incorporates a Finite Element Analysis (FEA) of the magnetic circuit and a Computational Fluid Dynamics (CFD) analysis of the fluid flow. A similar approach was presented in a previous publication in which an ideal behaviour of an MR damper (no effect of air bubbles) was investigated. The model has been modified in the current study to include the effect of air bubbles. The results were found to support the assumptions for the reasons of the failure symptoms of the current MR damper. The results are shown in a comparative way between the former and current studies to show the differences in flow parameters, namely: pressure, velocity and viscosity, in the faultless and faulty modes. The results indicate that the presence of air bubbles in MR dampers reduces the damper force considerably. Therefore, the effect of the high yield stress of MR fluids due to the magnetic field is reduced

    The shape โ€“ morphing performance of magnetoactive soft materials

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    Magnetoactive soft materials (MSMs) are soft polymeric composites filled with magnetic particles that are an emerging class of smart and multifunctional materials with immense potentials to be used in various applications including but not limited to artificial muscles, soft robotics, controlled drug delivery, minimally invasive surgery, and metamaterials. Advantages of MSMs include remote contactless actuation with multiple actuation modes, high actuation strain and strain rate, self-sensing, and fast response etc. Having broad functional behaviours offered by the magnetic fillers embedded within non-magnetic matrices, MSMs are undoubtedly one of the most promising materials in applications where shape-morphing, dynamic locomotion, and reconfigurable structures are highly required. This review article provides a comprehensive picture of the MSMs focusing on the materials, manufacturing processes, programming and actuation techniques, behaviours, experimental characterisations, and device-related achievements with the current state-of-the-art and discusses future perspectives. Overall, this article not only provides a comprehensive overview of MSMsโ€™ research and development but also functions as a systematic guideline towards the development of multifunctional, shape-morphing, and sophisticated magnetoactive devices

    Nanofluid Flow in Porous Media

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    Studies of fluid flow and heat transfer in a porous medium have been the subject of continuous interest for the past several decades because of the wide range of applications, such as geothermal systems, drying technologies, production of thermal isolators, control of pollutant spread in groundwater, insulation of buildings, solar power collectors, design of nuclear reactors, and compact heat exchangers, etc. There are several models for simulating porous media such as the Darcy model, Non-Darcy model, and non-equilibrium model. In porous media applications, such as the environmental impact of buried nuclear heat-generating waste, chemical reactors, thermal energy transport/storage systems, the cooling of electronic devices, etc., a temperature discrepancy between the solid matrix and the saturating fluid has been observed and recognized
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