Smart materials are kinds of designed materials whose properties are controllable with the application of external stimuli such as the magnetic field, electric field, stress, and heat. Smart materials whose rheological properties are controlled by externally applied magnetic field are known as magneto-rheological materials. Magneto-rheological materials actively used for engineering applications include fluids, foams, grease, elastomers, and plastomers. In the last two decades, magneto-rheological materials have gained great attention of researchers significantly because of their salient controllable properties and potential applications to various fields such as automotive industry, civil environment, and military sector. This article offers a recent progressive review on the magneto-rheological materials technology, especially focusing on numerous application devices and systems utilizing magneto-rheological materials. Conceivable limitations, challenges, and comparable advantages of applying these magn...

A state of art on magneto-rheological materials and their potential applications:

Magnetorheological elastomers (MREs) are a class of recently emerged smart materials whose moduli are largely influenced when exposed to an external magnetic field. The MREs are particulate composites, where micro-sized magnetic particles are dispersed inside a non-magnetic polymeric matrix. These elastomers are known for changing their mechanical and rheological properties in the presence of a magnetic field. This change in properties is widely known as the magnetorheological (MR) effect. The MR effect depends on a number of factors such as type of matrix materials, type, concentration and distribution of magnetic particles, use of additives, working modes, and magnetic field strength. The investigation of MREs’ mechanical properties in both off-field and on-field (i.e. absence and presence of a magnetic field) is crucial to deploy them in real engineering applications. The common magneto-mechanical characterization experiments of MREs include static and dynamic compression, tensile, and shear tests in both off-field and on-field. This review article aims to provide a comprehensive overview of the magneto-mechanical characterizations of MREs along with brief coverage of the MRE materials and their fabrication methods.

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A review on magneto-mechanical characterizations of magnetorheological elastomers

Stretchable and magneto-sensitive strain sensor based on silver nanowire-polyurethane sponge enhanced magnetorheological elastomer

Discrete particle simulations are used to study the shear rheology of dense, stabilized, frictional particulate suspensions in a viscous liquid, toward development of a constitutive model for steady shear flows at arbitrary stress. These suspensions undergo increasingly strong continuous shear thickening (CST) as solid volume fraction $\phi$ increases above a critical volume fraction, and discontinuous shear thickening (DST) is observed for a range of $\phi$. When studied at controlled stress, the DST behavior is associated with non-monotonic flow curves of the steady-state stress as a function of shear rate. Recent studies have related shear thickening to a transition between mostly lubricated to predominantly frictional contacts with the increase in stress. In this study, the behavior is simulated over a wide range of the dimensionless parameters $(\phi,\tilde{\sigma}$, and $\mu)$, with $\tilde{\sigma} = \sigma/\sigma_0$ the dimensionless shear stress and $\mu$ the coefficient of interparticle friction: the dimensional stress is $\sigma$, and $\sigma_0 \propto F_0/ a^2$, where $F_0$ is the magnitude of repulsive force at contact and $a$ is the particle radius. The data have been used to populate the model of the lubricated-to-frictional rheology of Wyart and Cates [Phys. Rev. Lett.{\bf 112}, 098302 (2014)], which is based on the concept of two viscosity divergences or \textquotedblleft jamming\textquotedblright\ points at volume fraction $\phi_{\rm J}^0 = \phi_{\rm rcp}$ (random close packing) for the low-stress lubricated state, and at $\phi_{\rm J} (\mu) < \phi_{\rm J}^0$ for any nonzero $\mu$ in the frictional state; a generalization provides the normal stress response as well as the shear stress. A flow state map of this material is developed based on the simulation results.

A constitutive model for simple shear of dense frictional suspensions

Hysteresis of the viscoelastic properties and the normal force in magnetically and mechanically soft magnetoactive elastomers: Effects of filler composition, strain amplitude and magnetic field

This work reports a new type of ballistic composite which is prepared by integrating the carbon nanotube-polystyrene ethyl acrylate (CNT/PSt-EA) based shear thickening fluid (C-STF) with Kevlar fabric. Because the rheological property of the PSt-EA based STF is significantly enhanced by the CNT, the C-STF/Kevlar offers better ballistic property than Kevlar fabric. The ballistic test indicated that the ballistic limit velocity ( v b l ) of Kevlar could be improved from 84.6 m/s to 96.5 m/s by impregnating the C-STF. Here, the optimum addition of CNT for C-STF/Kevlar is 1.0% and excessive CNT addition reduces the reinforcement effect. Besides, as the volume fraction of dispersed phase in STF increased from 53.5% to 58.5%, the v b l increased from 92.9 m/s to 99.5 m/s. The fabric layer number also plays a critical role in the ballistic property of C-STF/Kevlar. By combining the finite element analysis (FEA) results of ballistic impact with the quasi-static puncture and yarn pull-out results, the enhanced anti-impact mechanism is obtained. It is found that the friction coefficient between the yarns is strengthened and the bearing area of the fabric is increased by doping STFs, thereby the ballistic performance of Kevlar is improved. This work achieves the regulation of ballistic performance of Kevlar composites.

The CNT/PSt-EA/Kevlar composite with excellent ballistic performance

In this work we reported a novel graphite doped conductive magnetorheological plastomer (GMRP) with magnetic field dependent electro-conductivity. The conductivity of the GMRPs increased by increasing the content of the graphite particles, while it decreased with the graphite size. When the graphite content reached 15 wt%, the conductivity of GMRPs is approximately 10 000 times higher than the non-doped MRP. Because the iron particles in the GMRPs were magnetic, the conductivity of the GMRPs was magnetically sensitive. Upon applying a 780 mT magnetic field, the electric conductivity could increase about 1000 times larger than the one under zero magnetic field. A particle–particle resistance model was developed to investigate the influence of the magnetic field and graphite doping on the conductivity, and the fitting curve matched the experimental results very well. Finally, a magnetically controllable on–off switch based on GMRPs was proposed and its working mechanism was discussed.

Haoming Pang

Papers

The CNT/PSt-EA/Kevlar composite with excellent ballistic performance

Magnetic field dependent electro-conductivity of the graphite doped magnetorheological plastomers

The magneto-mechanical properties of off-axis anisotropic magnetorheological elastomers

The dynamic mechanical properties of magnetorheological plastomers under high strain rate

Magnetically tunable adhesion of composite pads with magnetorheological polymer gel cores