Magnetoactive Elastomers Research Articles

Magnetoactive elastomers with periodic and random microstructures

We investigate the behavior of magnetoactive elastomers (MAEs) with periodic and random distributions of circular and elliptical fibers. For the MAEs with periodic microstructures, we develop finite element models and determine the local fields as well as the effective properties of MAEs with rectangular and quasi-hexagonal unit cells. For the MAEs with random microstructures, we derive a closed-form expression for the effective response making use of a recently developed theory (Ponte Castañeda and Galipeau, 2011). In particular, we determine the responses to pure shear loading in the presence of a magnetic field, both of which are aligned with the geometric axes of the fibers, and examine the roles of the deformation, concentration, particle shape, and distribution on the magnetostriction, actuation stress, and the magnetically induced stiffness of the composite. We show that the coupling effects are of second order in the concentration. This is consistent with the fact that these effects are primarily the result of the interaction between inclusions. We also demonstrate explicitly that the magnetomechanical coupling of these MAEs, when subjected to aligned loading conditions, depends not only on the magnetic susceptibility, but also, crucially, on its derivative with respect to the deformation. As a consequence, we find that the magnetoelastic effects may be quite different, even for composites with similar effective susceptibilities.

Calculations of magnetoactive elastomer reactions in a uniform external magnetic field

The model of a magnetoactive elastomer (MAE) based on a system of single-domain fine particles distributed in an elastically deformable matrix is considered. The dependence of a deformation of samples with different concentrations of an ultra-dispersed magnetic material with a given value of a uniformly applied external magnetic field has been calculated and compared with experimental data. It is shown that the presence of inflection points is connected to the intrinsic characteristics of the magnetic filler. Changing the strength of the external magnetic field leads to an alteration of the total energy, and as a consequence promotes the restructuring of the particle distribution, which results in a non-uniform internal magnetic field. The theoretical analysis is found to agree with the experimental data.

Ultra-Soft PDMS-Based Magnetoactive Elastomers as Dynamic Cell Culture Substrata

Mechanical cues such as extracellular matrix stiffness and movement have a major impact on cell differentiation and function. To replicate these biological features in vitro, soft substrata with tunable elasticity and the possibility for controlled surface translocation are desirable. Here we report on the use of ultra-soft (Young’s modulus <100 kPa) PDMS-based magnetoactive elastomers (MAE) as suitable cell culture substrata. Soft non-viscous PDMS (<18 kPa) is produced using a modified extended crosslinker. MAEs are generated by embedding magnetic microparticles into a soft PDMS matrix. Both substrata yield an elasticity-dependent (14 vs. 100 kPa) modulation of α-smooth muscle actin expression in primary human fibroblasts. To allow for static or dynamic control of MAE material properties, we devise low magnetic field (≈40 mT) stimulation systems compatible with cell-culture environments. Magnetic field-instigated stiffening (14 to 200 kPa) of soft MAE enhances the spreading of primary human fibroblasts and decreases PAX-7 transcription in human mesenchymal stem cells. Pulsatile MAE movements are generated using oscillating magnetic fields and are well tolerated by adherent human fibroblasts. This MAE system provides spatial and temporal control of substratum material characteristics and permits novel designs when used as dynamic cell culture substrata or cell culture-coated actuator in tissue engineering applications or biomedical devices.

Giant field-induced strains in magnetoactive elastomer composites

Magnetoactive elastomers (MAEs) are composite materials consisting of nearly rigid, magnetically susceptible particles embedded in a soft, magnetically insensitive elastomer matrix. These multi-functional materials exhibit field-dependent strains and changes in stiffness. However, the strains that have been achieved experimentally to date are still relatively small (of the order of 1%). The reason for these small strains can be traced back to the dipolar nature of the forces between particles. Large particle concentrations are required to generate strong forces, but large concentrations also lead to large overall stiffness for the composite material, which, in turn, tends to reduce the overall strain. In this paper, we propose a new class of MAEs with doubly layered, herringbone-type microstructures capable of generating much larger field-induced strains of up to 100%. This is accomplished by combining the strong action of magnetic torques on suitably oriented magnetic layers, which interact directly with the applied magnetic field, together with the excitation of soft modes of simple shear deformation in the elastomer layers. Theoretical predictions, based on an exact analytical solution for the macroscopic magnetoelastic response of the materials, allow for the optimization of the microstructure for enhanced magnetostriction.

Evaluation of highly compliant magneto‐active elastomers with colossal magnetorheological response

ABSTRACTHighly compliant elastomers with a shear storage modulus as low as 25 Pa are prepared using commercially available silicone, plasticizer, and tactile mutator silicone additive. They are used as matrix material for magneto‐active elastomers (MAEs) with carbonyl iron contents between 0 and 85 wt %. In the absence of an external magnetic field, the storage modulus of MAEs based on two selected mixtures ranges between ∼100 Pa and ∼2000 Pa. Addition of a mutator to the matrix mixture results in a long post‐cure period depending on the curing temperature and the initial mixture. In the presence of a magnetic field, the presented MAEs exhibit a strong magneto‐induced change in storage modulus resulting in a colossal magnetorheological effect of &gt;106 % which is ∼30 times higher than previously reported values. The results are of interest in applications using such elastomers as cell substrates with magnetically tunable rigidity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39793.

Magnetodeformational effect of the magnetoactive elastomer and its possible applications

Magnetodeformational effect (deformation in non-uniform magnetic field) of magnetoactive elastomer has been studied experimentally. It has been shown that in non-uniform magnetic field this material is able to be reversibly deformed by 250%. In dynamic regimes the deformations under elongation are up to 80% while the ones under compression are 2%. Effective frequency range of the material is up to 100 Hz. As a possible application of the material a magneto controlled valve of flow rate (gas, liquid) was developed.

Magnetoresistive Effect in Magnetoactive Elastomers

A study of the influence of magnetic field on the resistivity of the magnetoactive (magnetorheological) elastomer has been conducted. The material consisted of a soft polymer matrix and magnetic fillers being powders of Fe, Ni, and the Fe–Nd–B alloy. Under the influence of the field with a value of 300 mT, the elastomer exhibited the magnetoresistive effect: The specific electric resistivity of the material was noticed to decrease by 3 orders. In addition, a significant dependency of the ability to conduct electric current was found on mechanical influence (piezoresistive effect) and combined influence of mechanical force and magnetic field. In the case considered, the behavior of the electroconductivity has a complex character.

Transversely isotropic nonlinear magneto-active elastomers

Magneto-active elastomers are smart materials composed of a rubber-like matrix material containing a distribution of magneto active particles. The large elastic deformations possible in the rubber-like matrix allow the mechanical properties of magneto-active elastomers to be changed significantly by the application of external magnetic fields. In this paper, we provide a theoretical basis for the description of the nonlinear properties of a particular class of these materials, namely transversely isotropic magneto-active elastomers. The transversely isotropic character of these materials is produced by the application of a magnetic field during the curing process, when the magneto active particles are distributed within the rubber. As a result the particles are aligned in chains that generated a preferred direction in the material. Available experimental data suggest that this enhances the stiffness of the material in the presence of an external magnetic field by comparison with the situation in which no external field is applied during curing, which leads to an essentially random (isotropic) distribution of particles. Herein, we develop a general form of the constitutive law for such magnetoelastic solids. This is then used in the solution of two simple problems involving homogeneous deformations, namely simple shear of a slab and simple tension of a cylinder. Using these results and the experimental available data we develop a prototype constitutive equation, which is used in order to solve two boundary-value problems involving non-homogeneous deformations—the extension and inflation of a circular cylindrical tube and the extension and torsion of a solid circular cylinder.

Magnetic Properties of Frozen Magneto-Active Elastomers

In the present paper we report temperature dependent magnetization measurements done on a magneto-active elastomers (MAEs) consisting of a siloxane rubber filled with carbonyl iron particles. The experiments performed in this study are similar to the conventional Zero-Field-Cooled and Field-Cooled magnetic tests. To the best of our knowledge, this approach, successfully used for studies on magnetic fluids, has never ever been applied to MAE. This test allowed us to reveal the effect of change of MAE structure under the action of an external magnetic field.

Experimental Validation of Numerical Methods of MRE Simulations

This paper deals with the development of magnetoactive elastomers (MREs) based on the carbonyl iron particles-filled polyurethane resin. Their stiffness can be changed easily by magnetic field. Such a property can be useful in construction of active vibration damping structural elements. For the needs of numerical modelling methods validation the elementary case of the two magnetic particles was investigated experimentally. Special “macro samples” were prepared with pairs of ferromagnetic particles of spherical shape of diameter of 12.7 mm. They provided easy observations and measurements. The gap distance between particles was established on the level of ¼ of the diameter. After application of the magnetic field particles started to attract each other like magnetic dipoles. The mutual displacement of the dipoles was recorded in function of the magnetic field intensity, which was varied in the range100÷300 [mT]. The deformation field was also obtained from the digital image processing (DIC). Then the experiment was simulated numerically with the use of the 3D FEM models. The dipoles were loaded by forces which were increased gradually until displacements reached values that were measured experimentally. Calculations were performed on the MSC Patran-MARC platform. The Neo-Hookean material model was used to describe properties of the resin matrix. Magneto-mechanical coupling was taken into consideration with the use of an iterative method. The results of calculations were compared with the experimental results. The validation of the base modelling concept was successfully completed.

Usage of magneto-active elastomers in a bumper of a vehicle for front impact protection

The control of the rigidity of the bumper can be provided by an application of magneto-active elastomers (MAE), capable to change their properties in a reversible and fast manner under the action of an applied magnetic field. The dependence of the energy taken away by the bumper at the impact on variable weight and rigidity has been found taking into account the presence of controllable MAE elements in the bumper construction. The calculated fields of pressure and deformations are necessary for optimization of a design, form and material of a forward panel of a bumper.

Magnetorheological effect of magneto-active elastomers containing large particles

The magnetorheological effect of elastomer composites containing a mixture of large (50-80 μm) and small (3-5 μm) particles has been experimentally examined. The data shows that elasticity in the range of small deformations (1%) for a magnetic field strength of 290 mT increased by two order of magnitude. This effect can be explained with the presence of the large particles in the structure of the composite assisting the aggregation effect. Due to the strong increase of the interparticle interaction compared with the restoring elastic forces, the presence of the large particles leads to the observed steep increase of Young's modulus.

Motion of ferroparticles inside the polymeric matrix in magnetoactive elastomers

Ferroelastic composites are smart materials with unique properties including largemagnetodeformational effects, strong field enhancement of the elastic modulus andmagnetic shape memory. On the basis of mechanical tests, direct microscopy observationsand magnetic measurements we conclude that all these effects are caused by reversiblemotion of the magnetic particles inside the polymeric matrix in response to an appliedfield. The basic points of a model accounting for particle structuring in a magnetoactiveelastomer under an external field are presented.

The damping device based on magnetoactive elastomer

The damping device based on magnetoactive elastomer

A new active noise abatement barrier system

In this contribution, a new active barrier system for windows, walls, and roofs to give noise abatement is introduced. The main concept was to induce desired mechanical vibration in the active object through electromagnetic excitation along its magneto-active boundary components. For this purpose, a new type of magneto-active elastomer profile was produced. The magneto-elastic excitation was used to produce desired vibrations to counteract the unwanted sound and noise. The magnetostriction or magnetizablity of the elastomeric boundary elements was achieved by an optimal combination of magnetic powders or fibers in the elastomer resin. The boundary rubber profile consisted of silicone rubber filled with 40% volume carbonyl iron powder. Consequently, the passive elastomer profile, which is normally used as a water/gas-tight element, was made magneto-active to act as a multifunctional body. As a feasibility study, experiments were performed on an acrylic plate with magneto-active boundary profiles. The motion was produced by a series of electromagnets placed along the rubber profiles. Several types of mechanical boundary conditions were used and, for each case, the vibration response under rectangular input signal was measured. A corresponding dynamic finite element simulation was also carried out. The experiments showed that by the use of a relatively small electrical energy input, pronounced mechanical vibrations with frequencies below 200 Hz could be produced. Depending on the specific application, the window system may be composed of single or multilayer, homogeneous or composite, flat or curved, transparent or non-transparent, thin or thick elements. In applications as a smart noise abatement window system, the motion of the active layer(s) should be regulated by a sensor, feedback, and control system. This system may find potential applications in intelligent skins, walls, roofs, containers, rooms, and other openings.

Magnetoactive elastomer composites

This paper deals with the development of magnetoactive elastomers and the exploration of some of their potential applications. In the course of material development, samples of particle-filled silicone rubber were produced and their mechanical and magnetic properties were experimentally determined. The test specimens consisted of pure and filled silicone with randomly dispersed as well as aligned magnetizable particle chains. To align the embedded particles in the elastomer, cross-linking of the resin took place in a magnetic field. Composite elastomer samples with different types of micron-size particles and various volume fractions were tested. Through alignment of the embedded particles, relative to pure silicone, the tensile strength increased by 80%, the tensile modulus by 200%, and the compression modulus by more than 300%. The maximum tensile strain of filled samples was generally reduced; however, samples with longitudinally aligned particles retained a relatively high strain capability as in the pure silicone rubber. Furthermore, to determine the active response of the composite, magnetic tests and coupled mechanical-magnetic experiments were performed. The magnetoactive elastomer composites produced and tested in this work demonstrated certain actuator force properties. The equivalent magnetic force calculated on the basis of these experiments and the magneto-solid mechanics theory showed the dependence of the magnetic force on the distribution of the particles in the elastomer. The elasto-magnetic behavior of beam samples was investigated by exposing the filled elastomer to the action of a permanent magnet at various gap distances, which led to the determination of a so-called magnetic bending stiffness. Moreover, through these experiments the influence of the particle alignment on the critical gap distance of the elasto-magnetic instability of composite elastomer was quantitatively estimated. The compression tests on cylindrical samples in the absence and the presence of a magnetic field showed that the magnetic field would increase the stiffness of the material. These experiments lead to useful hints regarding the use of such elastomer composites as tunable force structural elements.

FIELD DEPENDENCE OF VISCOELASTIC PROPERTIES OF MR ELASTOMERS

A magnetoactive elastomer made of micronic carbonyl iron particles, structured in elongated clusters and embedded in a silicon elastomer matrix is studied under traction both in static and dynamic modes. The application of a magnetic field of 120 kA/m induces a change in elastic moduli of about 0.6 MPa at strains of 4 to 5%. Still higher changes (4 MPa) are observed in dynamic storage modulus at low strains (10-4 to 10-3). The shape of the stress-strain curves are explained by taking into account the existence of a fiber like structure.