Giant Extensional Strain of Magnetoactive Elastomeric Cylinders in Uniform Magnetic Fields

Abstract

Elongations of magnetoactive elastomers (MAEs) under ascending–descending uniform magnetic fields were studied experimentally using a laboratory apparatus specifically designed to measure large extensional strains (up to 20%) in compliant MAEs. In the literature, such a phenomenon is usually denoted as giant magnetostriction. The synthesized cylindrical MAE samples were based on polydimethylsiloxane matrices filled with micrometer-sized particles of carbonyl iron. The impact of both the macroscopic shape factor of the samples and their magneto-mechanical characteristics were evaluated. For this purpose, the aspect ratio of the MAE cylindrical samples, the concentration of magnetic particles in MAEs and the effective shear modulus were systematically varied. It was shown that the magnetically induced elongation of MAE cylinders in the maximum magnetic field of about 400 kA/m, applied along the cylinder axis, grew with the increasing aspect ratio. The effect of the sample composition is discussed in terms of magnetic filler rearrangements in magnetic fields and the observed experimental tendencies are rationalized by simple theoretical estimates. The obtained results can be used for the design of new smart materials with magnetic-field-controlled deformation properties, e.g., for soft robotics.

Tunable Drop Splashing on Magnetoactive Elastomers

“…In the authors’ case, the variation of the shear modulus in the absence of a field was achieved by changing the ratio of the molar concentrations of vinyl and hydride groups in the initial compound by adding different doses of the hydride‐group containing component (crosslinker 210). [ 46,53 ] An increase in the stoichiometry, which was the ratio of the molar concentrations of hydride and vinyl reactive groups, leads to a stiffer polymer matrix, when the stoichiometry remains less than approximate unity. The cross‐linking reaction was activated by the Pt‐Catalyst 510 (0.067 wt%).…”

Magneto-Mechanical Coupling in Magneto-Active Elastomers

“…In order to clarify the common basis of the models presented in this section, Figure 2 can be used: it illustrates an MAE sample with a cylindrical shape which is frequently used in experiments [ 50 , 51 , 52 ]. In the vicinity of each material point, the microstructure is assumed to consist of stiff, magnetizable particles surrounded by a soft and non-magnetizable elastomer matrix.…”

“…Here, denotes the magnetization function, see Equation ( 1 ), defines the demagnetizing factor of a sample along its axis of symmetry and describes the actual, in general arbitrary or irregular, microstructure. This theoretical development allowed for quantifying the contribution of microstructure effect into the magnetically induced stress in confined MAE samples, as described in detail in [ 50 , 78 ]. Clear trends for the isotropic and structured samples have been established by fitting the theory predictions, see the right side of Figure 6 , to the measured stress data in a specially designed experiment [ 78 ].…”

Magnetorheological Response for Magnetic Elastomers Containing Carbonyl Iron Particles Coated with Poly(methyl methacrylate)

“…Magnetic elastomers are stimuli-responsive, soft materials [ 1 , 2 , 3 , 4 , 5 ], and their physical properties alter in response to magnetic fields. The magnetic response for a magnetic elastomer is in general drastic; therefore, the materials attract considerable attention as actuators in the next generation [ 6 , 7 , 8 , 9 , 10 ]. A magnetic elastomer consists of polymeric matrices such as polyurethane, and magnetic particles nanometers or micrometers in diameter.…”