Role of Magnetization Anisotropy in the Active Behavior of Magnetorheological Elastomers

2011 ◽  
Author(s):  
Paris R. von Lockette ◽  
Samuel E. Lofland
Keyword(s):  
Magnetic Field ◽  
Magnetic Particles ◽  
Shear Stiffness ◽  
Shape Anisotropy ◽  
Spherical Particles ◽  
Dynamic Shear ◽  
Soft Magnetic ◽  
Magnetorheological Elastomers ◽  
Particle Level

Magnetorheological elastomers (MREs) are a re-emerging class of smart materials whose novel behavior stems from their response to magnetic fields. Historically comprised of soft-magnetic carbonyl (spherical) iron particles embedded in highly compliant matrix materials, MRE research has focused on their apparent change in shear modulus (in excess of 60%) under a magnetic field. Recent work by the authors has departed from the experimental and theoretical focus on MREs made from soft-magnetic particles (S-MREs) to investigate MREs having hard-magnetic particle inclusions (H-MREs). While H-MRE materials do not perform well in dynamic shear stiffness applications when compared to the traditional S-MREs, H-MREs provide remotely powered, fully reversible actuation capabilities that S-MREs are unable to achieve. In addition, in the same dynamic shear stiffness applications these H-MREs provide a measure of active control of which S-MREs are also incapable. This work examines the role that particle magnetization, developed due to shape anisotropy, plays in the actuation response S-MREs in contrast to H-MREs. H-MRE response is predicated on the response of the hard-magnetic particles to the external magnetic field and to neighboring particles. Since hard-magnetic particles have an internal preferred magnetic orientation, they are able to generate torques at the particle level, T = M × B, where T is the torque density, M is the magnetization, and B is the local magnetic flux density. In contrast, soft-magnetic particles may develop an induced magnetization when exposed to an external field if the particles exhibit shape anisotropy. This induced magnetization is also capable of producing torque at the particle level, however, spherical particles like those historically used in MREs are geometrically isotropic and therefore do not develop induced magnetization either and consequently the widely studied MREs comprised of soft-magnetic spherical particles generate no torque at the particle level. Shape anisotropy further complicates the mechanical response by inducing Eshelby-type shape-dependent effects on the mechanical stresses developed local to the particle. These effects vary the local particle rotation, resulting from a given macroscopic loading, and in turn affect the local magnetic field by changing the particle’s magnetization axis with respect to the external field. The result is a material system whose elastomagnetic response depends on particle shape and orientation as well as on particle magnetization. In previous works the authors used barium hexaferrite (a hard magnetic material) and carbonyl iron powders to generate MRE materials having varying particle alignment and magnetization permutations. These materials were examined in cantilever bending modes to assess and differentiate their abilities as bending actuators. In this work, finite element studies mirroring the bending tests are performed to determine the role of particle/magnetization anisotropy on the behavior. Results show strong dependence on particle shape anisotropy.

Actuation Behavior in Patterned Magnetorheological Elastomers: Simulation, Experiment, and Modeling

2012 ◽  
Author(s):  
Paris von Lockette
Keyword(s):  
Magnetic Field ◽  
Smart Materials ◽  
Magnetic Particles ◽  
Constitutive Models ◽  
Barium Hexaferrite ◽  
Shear Stiffness ◽  
Silicone Elastomer ◽  
Dynamic Shear ◽  
Magnetorheological Elastomers ◽  
Magnetic Symmetry

Magnetorheological elastomers (MREs) are an emerging class of smart materials whose mechanical behavior varies in the presence of a magnetic field. Historically MREs have been comprised of soft-magnetic iron particles in a compliant matrix such as silicone elastomer. Numerous works have experimentally cataloged the MRE effect, or increase in shear stiffness, versus the applied field. Several other researchers have derived constitutive models for the large deformation behavior of MREs. In almost all cases the arrays of embedded particles, and or the particles themselves, are assumed magnetically symmetric with respect to the external magnetic field, i.e. the bulk materials exhibit magnetic symmetry in the given experimental or analytical configuration. In this work the author presents results of dynamic shear experiments, Lagrangian dynamic analysis, and static shear simulations on MRE material systems that exhibit broken magnetic symmetry. These new materials utilize barium hexaferrite powder as the magnetically anisotropic filler combined with a compliant silicone elastomer matrix. Simulations of representative laminate structures comprised of varied arrays of magnetic particles exhibit novel actuation behaviors including reversible shearing deformation, variable magnetostriction, and most surprisingly, piezomagnetism. Results of dynamic shear experiments and analytical modeling support predicted shearing actuation responses in MREs having broken symmetry and only in those systems.

Folding Actuation and Locomotion of Novel Magneto-Active Elastomer (MAE) Composites

2013 ◽  
Author(s):  
Paris von Lockette ◽  
Robert Sheridan
Keyword(s):  
Magnetic Field ◽  
Barium Ferrite ◽  
Magnetic Particles ◽  
Flat Surface ◽  
Iron Particles ◽  
Soft Magnetic ◽  
Magnetorheological Elastomers ◽  
Vibration Attenuation ◽  
Magnetically Aligned ◽  
Mechanical Actuation

Magneto-active elastomers (also called magnetorheological elastomers) are most often used in vibration attenuation application due to their ability to increase in shear modulus under a magnetic field. These shear-stiffening materials are generally comprised of soft-magnetic iron particles embedded in a rubbery elastomer matrix. More recently researchers have begun fabricating MAEs using hard-magnetic particles such as barium ferrite. Under the influence of uniform magnetic fields these hard-magnetic MAEs have shown large deformation bending behaviors resulting from magnetic torques acting on the distributed particles and consequently highlight their ability for use as remotely powered actuators. Using the magnetic-torque-driven hard-magnetic MAE materials and an unfilled silicone elastomer, this work develops novel composite geometries for actuation and locomotion. MAE materials are fabricated using 30% v/v 325 mesh barium ferrite particles in Dow Corning HS II silicone elastomers. MAE materials are cured in a 2T magnetic field to create magnetically aligned (anisotropic) materials as confirmed by vibrating sample magnetometry (VSM). Gelest optical encapsulant is used as the uniflled elastomer material. Mechanical actuation tests of cantilevers in bending and of accordion folding structures highlight the ability of the material to perform work in moderate, uniform fields of μ0H = 150 mT. Computational simulations are developed for comparison. Folding structures are also investigated as a means to produce untethered locomotion across a flat surface when subjected to an alternating field similar to scratch drive actuators; geometries investigated show promising results.

Defining and Investigating New Symmetry Classes for the Next Generation of Magnetorheological Elastomers

2009 ◽  
Author(s):  
Paris R. von Lockette ◽  
Samuel Lofland ◽  
Joseph Biggs
Keyword(s):  
Field Strength ◽  
Magnetic Particles ◽  
Barium Hexaferrite ◽  
Magnetic Behavior ◽  
Soft Magnetic ◽  
Magnetorheological Elastomers ◽  
Symmetry Classes ◽  
Particle Level ◽  
Particle Alignment ◽  
Beam Bending

This work addresses the fundamental difference in behavior between magnetorheological elastomers (MREs) formed from soft-magnetic particles, whose behavior is driven by local demagnetizing effects and those formed with hard-magnetic particles that have a preferred magnetic axis and therefore generate magnetic torques at the particle level. This work explores the phenomena by defining and examining four classes of MREs based upon permutations of particle alignment - magnetization pairs, i.e. I-I for magnetically isotropic particles arranged isotropically (randomly, or unaligned), A-A for magnetically anisotropic particles arranged anisotropically (typically aligned in chains), etc. The distinctions are important since the particle-field interactions for each class differ substantially. The behavior of classes I-I and I-A are driven primarily by demagnetizing effects while classes I-A and A-A are driven by the torques produced in the particles. MRE materials made with barium hexaferrite (BaM) (Classes A-A and I-A) and Fe powders (Classes A-I and I-I), aligned and unaligned, served as proxies for each of the four classes in this work. BaM, with saturation magnetization Msat = 4 × 105 A/m and coercive field Hc > 3 × 105 A/m, provided the magnetically anisotropic behavior while iron, with Msat = 1.8 × 106 A/m and Hc < 2 × 103 A/m, provided the soft magnetic behavior. Experiments on materials with 30% v/v particle concentrations showed that under uniform magnetic fields class A-A (aligned BaM) MREs were capable of large deflections in cantilever beam bending (deflections of 12mm for length 50mm and magnetic field 1.2 × 105 A/m) whereas all other classes, including I-A (random BaM) MREs, showed none. Tip deflection varied linearly with applied field strength. Tip blocking-force versus deflection experiments were also conducted on cantilevered A-A specimens. These tests showed that tip force increased with decreasing free deflection and with increasing field strength.

Magnetic tunneling junction based magnetic field sensors: Role of shape anisotropy versus free layer thickness

2011 ◽  
Vol 109 (7) ◽  
pp. 07C731 ◽  
Author(s):  
Lubna R. Shah ◽  
Nupur Bhargava ◽  
Sangcheol Kim ◽  
Ryan Stearrett ◽  
Xiaoming Kou ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Layer Thickness ◽  
Shape Anisotropy ◽  
Tunneling Junction ◽  
Free Layer ◽  
Magnetic Field Sensors ◽  
Magnetic Tunneling Junction ◽  
Magnetic Tunneling

MONITORING INTERPARTICLE DISTANCE IN MAGNETORHEOLOGICAL COMPOSITES

2007 ◽  
Vol 21 (28n29) ◽  
pp. 4868-4874
Author(s):  
G. BOSSIS ◽  
E. COQUELLE ◽  
C. NOEL ◽  
F. GIULIERI ◽  
A. M. CHAZE
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Energy Dissipation ◽  
Viscoelastic Properties ◽  
Magnetic Particles ◽  
Interparticle Distance ◽  
Magnetorheological Elastomer ◽  
Magnetorheological Elastomers ◽  
Magnetic Spheres ◽  
The Creation

We describe two different systems, the first one based on a magnetorheological elastomer and the second one on magnetic particles inside a liquid crystal. In both system we manage to have chain structures with particles that are not in contact. The effect of the gap between particles on the viscoelastic properties are studied. We show in particular how in magnetorheological elastomers, the energy dissipation is closely related to the creation and the motion of cavities in the gap between the particles. In liquid crystal chaining of particles can occur without applying a magnetic field. This happens if the anchoring of liquid crystal on the surface of the particles is homeotropic. We demonstrate how the combination of elastic defects and of a magnetic field allow to obtain microscopic springs made of a pair of magnetic spheres.

Sensing Behavior of Magnetorheological Elastomers

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Xiaojie Wang ◽  
Faramarz Gordaninejad ◽  
Mert Calgar ◽  
Yanming Liu ◽  
Joko Sutrisno ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electrical Properties ◽  
Magnetic Particles ◽  
External Stimulus ◽  
Magnetorheological Elastomer ◽  
Polymer Medium ◽  
Mechanical Loads ◽  
Magnetorheological Elastomers ◽  
Impedance Response ◽  
Ferromagnetic Particles

A magnetorheological elastomer (MRE) is comprised of ferromagnetic particles aligned in a polymer medium by exposure to a magnetic field. The structures of the magnetic particles within elastomers are very sensitive to the external stimulus of either mechanical force or magnetic field, which result in multiresponse behaviors in a MRE. In this study, the sensing properties of MREs are investigated through experimentally characterizing the electrical properties of MRE materials and their interfaces with external stimulus (magnetic field or stress/strain). A phenomenological model is proposed to understand the impedance response of MREs under mechanical loads and magnetic fields. Results show that MRE samples exhibit significant changes in measured values of impedance and resistance in response to compressive deformation, as well as the applied magnetic field.

Experimental study on tensile mechanical properties of magnetorheological fluid

2020 ◽  
Vol 34 (08) ◽  
pp. 2050070
Author(s):  
Weicheng Wang ◽  
Yiping Luo ◽  
Meng Ji
Keyword(s):  
Magnetic Field ◽  
Mechanical Properties ◽  
Tensile Stress ◽  
Magnetic Particles ◽  
Surface Characteristics ◽  
Magnetorheological Fluid ◽  
Maximum Tensile Stress ◽  
High Permeability ◽  
Soft Magnetic ◽  
The Magnetic Field

Magnetorheological fluid (MRF) is a kind of suspension composed of a nonconducting magnetic liquid and small soft magnetic particles with high permeability and low hysteresis. The tensile mechanical properties of MRF reflect its important mechanical properties. In this study, a testing device is designed to investigate the tensile mechanical properties of MRF in accordance with the plate method theory. First, the magnetic field is selected to analyze the influence of different gap sizes on the magnetic field. The magnetic field strength decreases as the gap increases. Second, a testing platform for tensile mechanical properties is built, and the tensile mechanical properties of MRF are experimentally studied under different magnetic field strengths, tensile speeds and surface characteristics. Experimental results show that the stronger the magnetic field, the greater the tensile yield stress. The maximum tensile stress at different velocities is nearly the same. Different surface characteristics affect tensile stress.

Line-patterned hybrid magnetorheological elastomer developed by 3D printing

2019 ◽  
Vol 31 (3) ◽  
pp. 377-388 ◽  
Author(s):  
AK Bastola ◽  
M Paudel ◽  
L Li
Keyword(s):  
Magnetic Field ◽  
3D Printing ◽  
Magnetic Particles ◽  
Dynamic Testing ◽  
Dynamic Properties ◽  
Magnetorheological Fluid ◽  
Magnetorheological Elastomers ◽  
3D Printed ◽  
Magnetorheological Effect ◽  
Printed Patterns

This article presents the development of line-patterned magnetorheological elastomers via 3D printing and their magnetorheological characterization. Herein, we consider five different patterns of magnetorheological fluid filaments that are printed and encapsulated within the elastomer matrix. The 3D-printed magnetorheological elastomers could represent the conventional isotropic and anisotropic magnetorheological elastomers. First, the effect of patterning the magnetorheological fluid filaments and the effect of change in the direction of the magnetic field is studied for all five patterns. Thereafter, the dynamic properties of 3D-printed magnetorheological elastomers under uniaxial deformation are presented. Magnetorheological effect shown by 3D-printed magnetorheological elastomers was found to be depended on the printed patterns as well as the direction of the applied magnetic field. This result showed that the 3D printing method has the potential to produce anisotropic magnetorheological elastomers or unique configuration of magnetic particles within the elastomer matrix. The dynamic testing showed that the storage modulus of 3D-printed magnetorheological elastomers is increased with increasing frequency and decreased with increasing strain amplitude, which signifies that the 3D-printed hybrid magnetorheological elastomers are also viscoelastic materials and the properties are magnetic field dependent as that of current magnetorheological elastomers.

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