Transient magnetorheological response of magnetoactive elastomers to step and pyramid excitations

Abstract

Transient rheological response of magnetoactive elastomers is experimentally studied using dynamic torsion at a fixed oscillation frequency in temporally stepwise changing magnetic fields and oscillation amplitudes. For step magnetic-field excitations, at least three exponential functions are required to reasonably describe the time behavior of the storage shear modulus over long time scales (>10(3) s). The deduced characteristic time constants of the corresponding rearrangement processes of the filler network differ approximately by one order of magnitude: τ1 ≲ 10(1) s, τ2 ∼ 10(2) s, and τ3 ∼ 10(3) s. The sudden imposition of the external magnetic field activates a very fast rearrangement process with the characteristic time under 10 s, which cannot be determined more precisely due to the measurement conditions. Even more peculiar transient behavior has been observed during pyramid excitations, when either the external magnetic field was first stepwise increased and then decreased in a staircase manner at a fixed strain amplitude γ or the strain amplitude γ was first stepwise increased and then decreased in a staircase manner at a fixed magnetic field. In particular, the so-called "cross-over effect" has been identified in both dynamical loading programs. This cross-over effect seems to be promoted by the application of the external magnetic field. The experimental results are discussed in the context of the specific rearrangement of the magnetic filler network under the simultaneous action of the external magnetic field and shear deformation. Striking similarities of the observed phenomena to the structural relaxation processes in glassy materials and to the jamming transition of granular materials are pointed out. The obtained results are important for fundamental understanding of material behavior in magnetic fields as well as for the development of devices on the basis of magnetoactive elastomeric materials.

Temperature-dependent magnetic properties of a magnetoactive elastomer: Immobilization of the soft-magnetic filler

“…1 it is seen that the hysteresis of the ()  GHdependence is observed in the entire region of the magnetization fields. Such hysteresis phenomena, including transient behavior, have been studied earlier, for example, in [44][45][46]. For the decreasing field H, the value of (0)  G is larger than the value of (0)  G for the initially non-magnetized MAE and the difference in these quantities turns out to be about 50% (see the inset in Fig 1.) At the subsequent ascending/descending branches of the magnetic field the value of (0)  G remains almost unchanged.…”

Magnetorheological Fluids Based on Star-Shaped and Linear Polydimethylsiloxanes

“…A significant hysteresis of the loss modulus is also observed when increasing and decreasing the magnetic field. It was previously noted that magnetomechanical hysteresis is a property inherent in magneto-polymer composites based on both crosslinked polymer matrices [39][40][41][42] and liquid dispersion media [29]. It is associated with the processes of rearrangement of the structure formed by microparticles of the magnetic filler which are determined not only by the magnitude of the magnetic field but also by the prehistory of evolution under simultaneous application of the field and mechanical load.…”

Nonlinear Magneto-Electro-Mechanical Response of Physical Cross-Linked Magneto-Electric Polymer Gel

“…With higher drop heights, the electrical conductivity recovers sooner. To characterize the recovery behaviors, the Prony series with one order was adopted (Belyaeva et al, 2016;Wen et al, 2018).…”