The evaluation and implementation of magnetic fields for large strain uniaxial and biaxial cyclic testing of Magnetorheological Elastomers

Abstract

Magnetorheological Elastomers (MREs) are "smart" materials whose physical properties are altered by the application of magnetic fields. In previous studies the properties of MREs have been evaluated under a variety of conditions, however little attention has been paid to the recording and reporting of the magnetic fields used in these tests [1]. Currently there is no standard accepted method for specifying the magnetic field applied during MRE testing. This study presents a detailed map of a magnetic field applied during MRE tests as well as providing the first comparative results for uniaxial and biaxial testing under high strain fatigue test conditions. Both uniaxial tension tests and equi-biaxial bubble inflation tests were performed on isotropic natural rubber MREs using the same magnetic fields having magnetic flux densities up to 206mT. The samples were cycled between pre-set strain limits. The magnetic field was switched on for a number of consecutive cycles and off for the same number of following cycles. The resultant change in stress due to the application and removal of the magnetic field was recorded and results are presented.

The evaluation of the effect of strain limits on the physical properties of Magnetorheological Elastomers subjected to uniaxial and biaxial cyclic testing

“…The MRE samples used in all tests reported in this paper are carbon black filled natural rubber based MREs from the same sample batch used to investigate the effect of magnetic flux density on the MR effect in an earlier study [1]. A number of previous studies by other researchers [7][8][9], focused on NR based MREs.…”

“…NR was chosen due to its superior physical (modulus) and a fatigue property, which is important for isolating the MR effect as with softer rubbers, such as silicone or urethane, the change from cycle to cycle may be attributable to fatigue effects in the matrix material. The test method is described in the previous study by the authors [1] with the same sample dimension for both the uniaxial and biaxial tests being used.…”

“…While anisotropic MREs provide greater MR properties when the magnetic field is applied parallel to the particle chains [4], the presence of the magnetic field during the curing process introduces an extra variable into the experimental results obtained from cyclic testing. For this reason isotropic MRE samples were used in the tests to ensure that any measured changes in their properties can be fully attributed to changes in test conditions and not changes in the sample particle distribution due to variations in the magnetic field applied during the curing process [1].…”

“…In particular, experimental results do not exist for MREs cycled at high strain for both uniaxial and biaxial conditions [1,11] The focus of this research is to investigate the influence of strain limits on the MR effect for MREs under cyclic uniaxial and biaxial loading. This is achieved by testing MREs under both uniaxial and biaxial loading conditions with similar strain limits and with the same applied magnetic field.…”

“…The tests were repeated with the same maximum strain but lower strain amplitudes. As the effective strain in biaxial tension for a specific strain limit is much higher than in the uniaxial case, a direct comparison of the properties (modulus) is impossible but trends can be compared [1].…”