Magnetorheological effect of magneto-active elastomers containing large particles (original) (raw)
Related papers
Magnetoactive elastomer composites
Polymer Testing, 2004
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 magnetosolid 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 elastomagnetic 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.
On the MagnetoElastic Properties of Elastomer-Ferromagnet Composites
2000
We study the macroscopic magneto-mechanical behavior of composite materials consistingof a random, statistically homogeneous distribution of ferromagnetic, rigid inclusions embeddedfirmly in a non-magnetic elastic matrix. Specifically, for given applied elastic and magnetic fields,we calculate the overall deformation and stress-strain relation for such a composite, correctto second order in the particle volume fraction. Our solution accounts for the fully coupledmagneto-elastic...
Basic magnetic properties of magnetoactive elastomers of mixed content
Smart Materials and Structures
The results of theoretical and experimental investigations of the polymer composites that belong to a class of magnetoactive elastomers with mixed magnetic content (MAEs-MC) are presented. The fundamental distinction of such composites from ordinary magnetoactive elastomers is that the magnetic filler of MAEs-MC comprises both magnetically soft (MS) particles of size 3–5 µm and magnetically hard (MH) particles whose size is an order of magnitude greater. Since MH particles of the magnetic filler are mixed into a composition in a non-magnetised state, this can ensure preparation of samples with fairly homogeneous distribution of the filler. The ‘initiation’ process of a synthesised MAE-MC is done by its magnetisation in a strong magnetic field that imparts to the sample unique magnetic and mechanical properties. In this work, it is shown that the presence of MS particles around larger MH particles, firstly, causes an augmentation of magnetic moments, which the MH particles acquire du...
Magnetic Hybrid-Materials
In this contribution, a magnetoactive elastomer (MAE) of mixed content, i.e., a polymer matrix filled with a mixture of magnetically soft and magnetically hard spherical particles, is considered. The object we focus on is an elementary unit of this composite, for which we take a set consisting of a permanent spherical micromagnet surrounded by an elastomer layer filled with magnetically soft microparticles. We present a comparative treatment of this unit from two essentially different viewpoints. The first one is a coarse-grained molecular dynamics simulation model, which presents the composite as a bead-spring assembly and is able to deliver information of all the microstructural changes of the assembly. The second approach is entirely based on the continuum magnetomechanical description of the system, whose direct yield is the macroscopic field-induced response of the MAE to external field, as this model ignores all the microstructural details of the magnetization process. We find that, differing in certain details, both frameworks are coherent in predicting that a unit comprising magnetically soft and hard particles may display a nontrivial reentrant (prolate/oblate/ prolate) axial deformation under variation of the applied field strength. The flexibility of the proposed combination of the two complementary frameworks enables us to look deeper into the manifestation of the magnetic response: with respect to the magnetically soft particles, we compare the linear regime of magnetization to that with saturation, which we describe by the Fröhlich-Kennelly approximation; with respect to the
Dynamic behavior of thick magnetorheological elastomers
SPIE Proceedings, 2012
This work is focused on the study of the dynamic behavior of thick magnetorheological elastomers at high frequencies. Experimental and theoretical studies are conducted to investigate the dynamic shear properties of magnetorheological elastomers which are affected by increasing the thickness, as well as the percentage of iron particles contained in magnetorheological elastomers. A double-shear test setup is designed and built to test the magnetorheological elastomer samples over a range of frequencies from 200 to 800 Hz. The results demonstrate that the thickness of magnetorheological elastomer significantly affects the material properties in the off-state, that is, when no magnetic field is applied. However, for the on-state, when the material is activated by a magnetic field, the thickness of the sample does not show a significant effect on the change in storage modulus induced by a magnetic field. The theoretical analysis includes a macromechanical model for the storage modulus and loss modulus of magnetorheological elastomer as a function of thickness, percentage of iron particles, and applied magnetic field. Comparisons between the theoretical and experimental results show that the model reasonably predicts the dynamic behavior of thick magnetorheological elastomers.
Selected Magnetomechanical Properties of Magnetorheological Elastomers
2012
The goal of the paper is to present the process of preparing magnetorheological composite materials with thermoplastic matrices called magnetorheological elastomers (MRE) and the possibilities of modelling them using KevinVoight relations. At the beginning, the MRE components are presented: a specific thermoplastic elastomer matrix material and ferromagnetic fillers. Both polymer and iron particles are mixed together in specific proportions on the basis of of calculations of the Criti� cal Particle Volume Concentration. Moreover, the method of mixing and the process parameters are described in this paper as they are crucial to achieve the desired structure of the composite. The next important step in testing the MR elastomer is preparation of the sample. At the beginning, the material samples are cut and mounted in such away as to be able to test the influence of magnetic and mechanical fields. Such material is cut into pieces and glued between claddings that support it dur� ing tes...
Mechanical properties of magnetorheological elastomers under shear deformation
Composites Part B: Engineering, 2012
In this paper, urethane magnetorheological elastomers (MREs) consisting of carbonyl-iron particles in a polyurethane matrix were studied. The volume fraction of particles was equal to 11.5%. Three types of ferromagnetic particles were used, with average particle size ranging from 1 to 70 lm. The elastic (storage) modulus G 0 was measured as a function of angular frequency x and strength of magnetic field. The measured G 0 values were approximated with empirical model. The highest magnetorheological effect has been found for samples with 6-9 lm carbonyl-iron powder. The highest increase in the yield stress is observed for samples with particles aligned at 30°to the magnetic field lines. It has been found that rheological properties strongly depend on the MRE microstructure, in particular on the size/shape of particles and their arrangement. By optimizing the particles size, shape and alignment, the stiffness of MREs has been increased under applied magnetic field.