Magnetorheology: Advances and Applications: Volume 6 - Rilegato

Rilegato

ISBN 10: 1849736677 ISBN 13: 9781849736671

Casa editrice: Royal Society of Chemistry, 2013

Riassunto

Magnetorheological fluids, smart fluids which change viscosity in the presence of a magnetic field, are of great commercial interest for many engineering applications such as shock absorbers and dampers in aerospace.

Magnetorheology: Advances and Applications provides an update on the key developments in the physics, chemistry and uses of magnetorheological fluids. Topics covered include the role of interparticle friction and rotational diffusion, magnetoelasticity, nondimensional flow analysis, thin-film rheology, tribology, coated magnetorheological composite particles and magnetorheological devices with multiple functions. Specific chapters on applications cover adaptive magnetorheological energy absorbing mounts for shock mitigation, magnetorheological fluid-based high precision finishing technologies, adaptive magnetorheological landing gear systems and magnetorheological lag dampers for stability augmentation in helicopters.

Edited by a leading expert and with contributions from distinguished scientists in the field this timely book is suitable for chemists, physicists and engineers wanting to gain a comprehensive overview of these smart materials.

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Informazioni sugli autori

Dr. Wereley holds a B.Eng. (Honors) in Mechanical Engineering from McGill University, Montreal, Canada, and M.S. and Ph.D. in Aeronautics and Astronautics from the Massachusetts Institute of Technology in 1987 and 1990, respectively. He joined the Alfred Gessow Rotorcraft Center, University of Maryland in 1993 and currently serves there as the Director of the Smart Structures Laboratory and the Composites Research Laboratory. His research interests are in dynamics and control of smart structures, with emphasis on active and passive vibration isolation and shock mitigation applied primarily to rotorcraft as well as other aerospace and automotive systems. Dr. Wereley has published (or at press) over 140 journal articles, 10 book chapter contributions, and over 230 conference articles. Dr. Wereley is the Editor of the Journal of Intelligent Material Systems and Structures (2007 - present) and serves as an associate editor for the Institute of Physics' journal Smart Materials and Structures and AIAA Journal. His awards include ASME Adaptive Structures and Adaptive Materials Best Paper Award (2004), AIAA National Capital Section Engineer of the Year (2009). A. James Clark School of Engineering Faculty Service Award (2010), AIAA Sustained Service Award (2011), Harry T. Jenson Award (May 2011) from the American Helicopter Society for contributions to active crash protection systems for helicopters (team award with Boeing, US Army, Honeywell and University of Maryland). He was also awarded the ASME Adaptive Structures and Materials Systems Prize (2012) for his contributions to the physics and applications of magnetorheological fluids.

Dr. Wereley holds a B.Eng. (Honors) in Mechanical Engineering from McGill University, Montreal, Canada, and M.S. and Ph.D. in Aeronautics and Astronautics from the Massachusetts Institute of Technology in 1987 and 1990, respectively. He joined the Alfred Gessow Rotorcraft Center, University of Maryland in 1993 and currently serves there as the Director of the Smart Structures Laboratory and the Composites Research Laboratory. His research interests are in dynamics and control of smart structures, with emphasis on active and passive vibration isolation and shock mitigation applied primarily to rotorcraft as well as other aerospace and automotive systems. Dr. Wereley has published (or at press) over 140 journal articles, 10 book chapter contributions, and over 230 conference articles. Dr. Wereley is the Editor of the Journal of Intelligent Material Systems and Structures (2007 - present) and serves as an associate editor for the Institute of Physics' journal Smart Materials and Structures and AIAA Journal. His awards include ASME Adaptive Structures and Adaptive Materials Best Paper Award (2004), AIAA National Capital Section Engineer of the Year (2009). A. James Clark School of Engineering Faculty Service Award (2010), AIAA Sustained Service Award (2011), Harry T. Jenson Award (May 2011) from the American Helicopter Society for contributions to active crash protection systems for helicopters (team award with Boeing, US Army, Honeywell and University of Maryland). He was also awarded the ASME Adaptive Structures and Materials Systems Prize (2012) for his contributions to the physics and applications of magnetorheological fluids.

Dalla quarta di copertina

Magnetorheological fluids, smart fluids which change viscosity in the presence of a magnetic field, are of great commercial interest for many engineering applications such as shock absorbers and dampers in aerospace.

Magnetorheology: Advances and Applications provides an update on the key developments in the physics, chemistry and uses of magnetorheological fluids. Topics covered include the role of interparticle friction and rotational diffusion, magnetoelasticity, nondimensional flow analysis, thin-film rheology, tribology, coated magnetorheological composite particles and magnetorheological devices with multiple functions. Specific chapters on applications cover adaptive magnetorheological energy absorbing mounts for shock mitigation, magnetorheological fluid-based high precision finishing technologies, adaptive magnetorheological landing gear systems and magnetorheological lag dampers for stability augmentation in helicopters.

Edited by a leading expert and with contributions from distinguished scientists in the field this timely book is suitable for chemists, physicists and engineers wanting to gain a comprehensive overview of these smart materials.

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Magnetorheology

Advances and Applications

By Norman Wereley

The Royal Society of Chemistry

Copyright © 2014 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-84973-667-1

Contents

Chapter 1 Importance of Interparticle Friction and Rotational Diffusion to Explain Recent Experimental Results in the Rheology of Magnetic Suspensions G. Bossis, P. Kuzhir, M. T. López-López, A. Meunier and C. Magnet, 1, 
Chapter 2 Magnetorheology of Fe Nanofibers Dispersed in a Carrier Fluid R. C. Bell, D. T. Zimmerman and N. M. Wereley, 31, 
Chapter 3 Magnetoelasticity M. Zrinyi, 56, 
Chapter 4 MR Fluids at the Extremes: High-Energy and Low-Temperature Performance of LORD® MR Fluids and Devices Daniel E. Barber, 74, 
Chapter 5 Surface Effect on Flow of Magnetorheological Fluids: Featuring Modified Mason Number Barkan Kavlicoglu, Faramarz Gordaninejad and Xiaojie Wang, 96, 
Chapter 6 Thin-film Rheology and Tribology of Magnetorheological Fluids Juan de Vicente and Antonio J. F. Bombard, 142, 
Chapter 7 Coated Magnetorheological Composite Particles: Fabrication and Rheology Ying Dan Liu and Hyoung Jin Choi, 156, 
Chapter 8 Micro structures and Physics of Super-Strong Magnetorheological Fluids R. Tao, 179, 
Chapter 9 Magnetorheological Fluids Flowing Through Porous Media: Analysis, Experimental Evaluation, and Applications Norman M. Wereley, Wei Hu and Ryan Robinson, 206, 
Chapter 10 MR Devices with Advanced Magnetic Circuits Holger Böse, Johannes Ehrlich and Thomas Gerlach, 229, 
Chapter 11 Magnetorheological Fluid-Based High Precision Finishing Technology W. I. Kordonski, 261, 
Chapter 12 Adaptive Magnetorheological Energy Absorbing Mounts for Shock Mitigation Norman M. Wereley, Harinder J. Singh and Young-Tai Choi, 278, 
Chapter 13 Semi-Active Isolation System Using Self-Powered Magnetorheological Dampers Young-Tai Choi, Hyun Jeong Song, Wei Hu and Norman M. Wereley, 288, 
Chapter 14 Controllable Magnetorheological Damping in Advanced Helicopter Rotors Grum T. Ngatu, Wei Hu, Norman M. Wereley, Curt S. Kothera and Gang Wang, 307, 
Chapter 15 Magnetorheological Devices with Multiple Functions Wei-Hsin Liao, Chao Chen and Hongtao Guo, 342, 
Chapter 16 A Novel Medical Haptic Device Using Magnetorheological Fluid Seung-Bok Choi, Phuong-Bac Nguyen and Jong-Seok Oh, 363, 
Subject Index, 382, 

CHAPTER 1

Importance of Interparticle Friction and Rotational Diffusion to Explain Recent Experimental Results in the Rheology of Magnetic Suspensions

G. BOSSIS, P. KUZHIR, M. T. LÓPEZ-LÓPEZ, A. MEUNIER AND C. MAGNET

1.1 Introduction

Magnetorheological (MR) fluids are suspensions of magnetized micron-sized particles in a dispersing liquid. When an external magnetic field is applied, the particles acquire magnetic moments, attract to each other due to dipolar forces and form anisotropic aggregates aligned preferably with the magnetic field direction. Thus, upon a field application MR fluids undergo a reversible jamming responsible for a several order of magnitude increase in effective viscosity and appearance of a yield stress – threshold mechanical stress required for onset of flow. This phenomenon, referred to as magnetorheological effect, is being effectively used in numerous smart engineering applications. Enhancement of the MR effect and/or reduction of the size of the MR devices are important problems for these applications. One of the possible solutions of such problems consists of using rod-like magnetic particles, which produce a higher MR response as compared to spherical particles. Another solution consists of changing the orientation of an external magnetic field relative to the direction of the MR fluid flow. In this chapter we aim to describe physical mechanisms of the MR effect in the suspensions of rod-like magnetic particles (called hereinafter magnetic fiber suspensions) as well as in conventional MR suspensions (composed of spherical particles) subjected to a magnetic field longitudinal to the flow direction.

New MR fluids based on magnetic micro- and nano-fibers have been developed during last few years using different techniques, such as iron electro-deposition in alumina membranes, chemical precipitation of an iron salt followed by aging in the presence of a magnetic field, reduction of cobalt and nickel ions in polyols. The magnetic fiber suspensions have shown better sedimentation stability and developed a yield stress much larger than the one of the suspensions of spherical particles at the same magnetic field intensities and the same particle volume fraction. Such enhanced magnetorheological effect in fiber suspensions can be explained in terms of the interfiber solid friction and by enhanced magnetic permeability of these suspensions as compared to the permeability of conventional MR fluids. Both these effects are reviewed in detail in the present publication. Note that the similar particle shape effect has been observed in electrorheological (ER) fluids and was attributed to both the physical overlapping of the elongated particles (unavoidably leading to the interparticle friction) and to their strong dielectric properties.

Concerning the effect of the magnetic field orientation on the MR response of conventional MR fluids, it should be mentioned that most of the studies were focused on their flows in the presence of the magnetic field perpendicular to the flow – presumably, the case of the largest practical interest. In such geometry, the particle structures are formed perpendicularly to the flow direction, they oppose a large hydraulic resistance to the flow and generate a relatively high dynamic yield stress. In magnetic fields parallel to channel walls, the particle aggregates are expected to be oriented along the stream-lines and be (in theory) infinitely long because they are not subjected to tensile hydrodynamic forces. In such conditions, the suspension should undergo a Newtonian behavior and a certain decrease of its viscosity could be expected. This expectation is only confirmed for the suspensions composed of weakly paramagnetic particles, such as human red blood cells, which do not belong to the class of MR fluids. However, for conventional MR fluids, composed of strongly magnetizable particles, the stress level in parallel fields is relatively high and the MR fluid develops a strong Bingham behavior, which does not corroborate with the assumption of alignment of aggregates in flow direction. Such a strong "longitudinal" MR effect has recently been explained by stochastic rotary oscillations of the aggregates caused by many-body magnetic interactions with neighboring aggregates. The inter-aggregate interactions are accounted for by an effective rotational diffusion process with a diffusion constant proportional to the mean square interaction torque – a net magnetic torque exerted to a given aggregate by all the neighboring aggregates. Such a mechanism is reviewed in details in the present chapter.

The present chapter is organized as follows. In Section 1.2, we consider the microstructure (Section 1.2.1) and the rheology of magnetic fiber suspensions. Both effects of interparticle solid friction (Section 1.2.2) and the hydrodynamic interactions in the fiber suspension (Section 1.2.3) are thoroughly reviewed. The non-linear viscoelastic response of these suspensions developed in a large amplitude oscillatory shear (LAOS) flow is described in Section 1.2.4. Section 1.3 is devoted to the flow of a conventional MR fluid (composed of spherical particles) in the longitudinal magnetic field. A rotational diffusion concept is employed to explain an unexpectedly strong MR response in such geometry. Finally the conclusions and perspectives are outlined in Section 1.4.

1.2 Magnetic Fiber Suspensions

In this section, we consider shear deformation and shear flow of suspensions composed of cobalt micron-sized fibers synthesized via the polyol method described in detail by López-López et al. Anisotropic growth in the synthesis of cobalt fibers was induced by means of the application of a magnetic field during the whole synthesis time. Cobalt fibers were polydisperse with average length and width of 60 [+ or -] 24 mm and 4.8 [+ or -] 1.9 mm, respectively, as shown by SEM microscopy [Figure 1.1]. Cobalt spheres with an average diameter of 1.34 [+ or -] 0.40 mm were also synthesized in order to compare their MR response to the one of the cobalt fibers. The important feature of both types of particles is that their bulk magnetic properties are essentially the same, independently of their morphology. So, an enhanced magnetic permeability of the fiber suspensions, mentioned in Section 1.1, is explained by a weaker demagnetizing field inherent to fibers (as compared to spherical particles) due to their elongated shape. It is clear that the rheological response of the magnetic fiber suspension depends on its micro-structure developed under magnetic fields. So, the starting point of the present section will be visualization and analysis of the suspension microstructure in the absence of flows.

1.2.1 Microstructure

Some photos of planar structures of diluted suspensions of cobalt fibers (solid concentration 0.1 vol%) confined between two parallel glass slides (the gap was fixed to 0.15 mm) are shown in Figure 1.2. As is seen in Figure 1.2(a), in the absence of magnetic field the fibers form an entangled network with approximately isotropic orientation of fibers, and even at low fiber concentration (0.1 vol%), each fiber seems to have at least a few contact points with the neighboring ones. It can also be observed that individual fibers are gathered together in aggregates. Such aggregation in the absence of magnetic field could be due to the combination of different effects: (1) magnetic attraction between fibers because of their remnant magnetization [Mr = 53 kA m-1]; (2) short range van-der-Waals interaction; and (3) mechanical cohesion between rough fiber surfaces. Such cohesion is likely due to the solid friction between fibers and could involve an important contribution to the flocculation of the fiber suspension, as reported by Mason, Schmid et al. and Switzer and Klingenberg.

When a magnetic field parallel to the glass slides is applied, the fiber network becomes deformed and approximately aligned with the field direction [Figure 1.2(b)]. Notice that the fiber network remains entangled, the fibers are linked to the neighboring ones and, therefore, there is no complete alignment with the field. This can be explained by appearance of the solid friction between fibers, which hinders their motion and does not allow them to get completely aligned with the field. Hence, the structure observed is not at equilibrium. Otherwise, without friction, the free energy of the fiber suspension would have been minimized, and a structure with all the fibers aligned completely with the magnetic field, joined end by end with the neighboring ones, would have been observed. A zoomed view of the fiber network upon magnetic field application is presented in Figure 1.2(c). As observed, the fibers are rather polydisperse and have an irregular rough surface. They are linked to each other either by their extremities or by their lateral sides. In the latter situation, two contacting fibers either are attached by their lateral sides or cross each other at some angle. It seems that any type of interfiber contact is equiprobable.

Alternatively, when a magnetic field normal to the glass slides is applied, the fibers tend to become aligned in the vertical plane, i.e. transversely to the glass slides [Figure 1.2(d)]. However, as can be observed, some fiber aggregates are so big that they cannot be aligned in the vertical plane because their movement is restricted by the gap between the glass slides. And even smaller fiber aggregates do not get strictly perpendicular to the glass slides – fibers are always attached to the neighboring ones by magnetic and friction forces. Note that this structure is rather different from the column-like structure observed in suspensions of spherical magnetic particles. Notice also that when this fiber suspension is sheared (the upper glass slide is displaced horizontally), under the presence of a vertical magnetic field, the fiber aggregates get more oriented in the direction of shear [Figure 1.2(e)]. Thus, we believe that upon magnetic field application, the fibers gather into aggregates, which span the gap between the glass slides, and they are tilted, when sheared, in the direction of the shear.

Finally, a photo of a 3D structure of a model fiber suspension consisting of steel rods (15 mm in length and 1 mm in diameter) in silicone oil, in the presence of an applied magnetic field, is shown in Figure 1.2(f). Similarly to the planar structures discussed above, the fibers form a dendrite-like structure oriented preferably along the magnetic field lines. As seen in Figure 1.2(f), most of the contacts between fibers are either side-by-side or side-by-end, while end-by-end contacts are infrequent. In fact, this model structure shown in Figure 1.2(f) is quite similar to the structure shown in Figure 1.2(c). In both cases the fibers can either attach to neighboring ones by their lateral side (line contact) or cross each other at a certain angle (point contact).

The existence of different types of interfiber contacts is an essential point that must be taken into account to theoretically model the magnetorheology of suspensions of magnetic fibers. This is done in Section 1.2.2, where we introduce a microstructural model for magnetic fiber suspensions and explain the enhanced MR response of these suspensions in terms of interfiber solid friction. Theoretically determined static yield stress of the fiber suspension is compared to the measured one obtained from experiments on quasi-static shear deformation of the suspension.

1.2.2 Rheology: Interparticle Friction and Static Yield Stress

Let us consider a suspension of identical magnetic fibers confined between two infinite plates. The distance between these plates is supposed to be much larger than the fiber length. When the magnetic field is applied normally to the plates, the fibers attract each other and form some kind of anisotropic network. Precise details of such a network may only be predicted by particle level numerical simulations. To gain the first insight into the rheology of the magnetic fiber suspension, we impose artificially a stochastic near-planar suspension structure, which seems to be rather close to the one observed in experiments [Figure 1.2]. In more detail, we suppose that all the fibers lie more or less in planes parallel to the shear plane. Thus, the fiber suspension can be represented as a series of sheets, each one parallel to the shear plane, and containing stochastically oriented fibers, as depicted in Figure 1.3(a). The suspension is sheared by a displacement of the upper plate, and the strain angle is Θ. We shall calculate the stress vs. strain dependency and the suspension yield stress under the following considerations:

1. The fibers are supposed to not to slip over the plates.

2. The magnetic dipolar forces acting between fibers are negligible according to Kuzhir et al. and the only forces exerted on the fibers are the contact forces.

3. Most of the contact points are located on the lateral fiber surface rather than at the fiber extremities.

4. The surface of the fibers is rough [cf. Figure 1.1]. When the suspension is sheared, all the fibers slide over each other and exert friction forces on the neighboring fibers. In general, the value of these forces should depend on the shear rate. However, at low shear rates, considered in this section, a boundary lubrication regime between rough fiber surfaces is expected. In this regime, the friction forces appear to be independent of speed and are supposed to follow the Coulomb's friction law, [Florin]τ = [xi][Florin]n with [xi] being the friction coefficient and [Florin]n the normal force exerted by a neighboring fiber to a given fiber. At higher shear rates, considered in Section 1.2.3, the surface roughness generates a lifting force leading to hydrodynamic lubrication between fibers with the friction force proportional to the shear rate.

5. The contact forces between fibers belonging to different sheets are entirely defined by interparticle magnetic forces. Since the latter are neglected, the former should also be negligible. Therefore both the normal force [Florin]n and the friction force [Florin]τ are supposed to belong to the shear yz-plane and the friction force is assumed to be longitudinal with the fiber major axis.

The mechanical stresses arising in strained fiber suspensions are due to contact forces acting on fibers and the latter are, to a large extent, determined by the balance of torques. The projection of torques (exerted to a given fiber) onto the shear yz-plane reads:

[MATHEMATICAL EXPRESSION OMITTED] (1.1)

where s is the distance between the center of the given fiber and the contact point; the summation in second term of the left-hand side of eqn (1.1) is performed over all contact points of a given fiber; Tm is the magnetic torque exerted by the external magnetic field to a given fiber; the expression for this torque reads:

[MATHEMATICAL EXPRESSION OMITTED] (1.2)

where H is the internal magnetic field, θ is the angle between a given fiber and the magnetic field vector [Figure 1.3(a)], Vf = 2πa2l is the volume of the fiber, a and l are the fiber radius and semi-length, respectively, Xf is the fiber magnetic susceptibility, and μ0 = 4π10-7 Henry m-1 is the magnetic permeability of vacuum.

(Continues...)

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Dettagli dell'edizione

• Editore: Royal Society of Chemistry
• Data di pubblicazione: 2013
• Lingua: Inglese
• ISBN 10: 1849736677
• ISBN 13: 9781849736671
• Rilegatura: Copertina rigida
• Numero di pagine: 396
• Redattore: Wereley Norman
• Contatto del produttore: non disponibile
• Persona responsabile: non disponibile