The impact of CIP content on the field-dependent dynamic viscoelastic properties of MR gels

Stiffness enhancement of magnetorheological foam by structural modification using silica nanoparticles additive

Magnetorheological (MR) foam is a newly developed porous smart material that is able to change its properties continuously, actively, and reversibly in response to controllable external magnetic stimuli. Unfortunately, the stiffness or also known as storage modulus of MR foam is still rather low and insufficient, in the range of below 100 kPa only, due to weak interparticle interaction between CIPs and the foam matrix, which consequently restricts the potential of MR foam to be used in future sensor applications or in other semi-active devices. Therefore, the aim of this research is to enhance the structural and storage modulus of MR foam by adding silica nanoparticles as an additive. Consequently, MR foam samples with different compositions of silica nanoparticles in the range of 0–5 wt% were prepared via an in situ method. The rheological properties were tested under an oscillatory shear mode with the absence and presence of magnetic fields using a rheometer, with the input parameters of strains between 0.001% and 10% and range of magnetic flux density between 0 and 0.73 T for a magnetic field sweep test. The rheological findings show that with the addition of silica nanoparticles, particularly at 4 wt%, have enhanced the storage modulus of MR foam by 260%, which attributed to the highest stiffness from 45 to 162 kPa. Meanwhile, the change of storage modulus under the influence of magnetic fields (0 T–0.73 T) somehow showed small increment, about ∆1 kPa for each concentration of silica nanoparticles in MR foams, due to non-magnetic behavior of silica. The morphological characteristics of MR foams were described by an elemental analysis carried out by a using variable pressure scanning electron microscope (VPSEM) equipped with energy dispersive x-ray spectroscopy (EDX). The micrographs demonstrated large open-cell pores for MR foam, while MR foam with silica nanoparticles exhibited more closed-cell pores, associated with the enhancement of its storage modulus. It indicates that the silica nanoparticles have encouraged well dispersion of the particles in the foam matrix, which improved and strengthened the microstructure of MR foams through formation of silane coupling bonds of silica in the filler-matrix structure. Overall, incorporation of silica nanoparticles as an additive in the MR foam could provide advantage in enhancing the structure and mechanical properties of MR foam, for various future smart devices.

Analysis of Damping Characteristics of Magnetorheological Damper under Impact Load

Compared to magnetorheological fluid, magnetorheological gel has better anti-settling performance and stability. Therefore, magnetorheological gel is suitable for devices that can meet operational requirements in all aspects after long-term storage, such as the anti-recoil application of weapons. To study this in-depth, the mechanism of the influence of magnetorheological gel micro-magnetic-mechanical properties on the macro-output damping mechanics of the damper, a parallel plate model of the mixed flow mode composed of Couette shear flow and Poiseuille pressure flow was established. The theoretical analysis was of the output damping of the damper. Finally, the controllability of the damper under impact load employed magnetorheological gel was preliminarily analyzed. The results indicate that the damping coefficient of the damper increases with the increase of dynamic viscosity ηB of the magnetorheological gel, piston effective cross-sectional area AP, magnetic pole L, and Bingham coefficient Bi. Magnetorheological damper has controllability under impact load and can reach a wide controllable range under the condition under small magnetic field ranging from 0 mT to 131 mT.

Experimental investigation on the influence of temperature on the hysteresis behavior of magnetorheological gel by employing a large-amplitude-oscillation-shear test method

It is of great significance to explore the mechanism of temperature influence on magnetorheological gel before employing materials for device design. Because of the temperature of the materials rising by the coil during the working process, the wall sliding effect, the interaction between the particles and the interaction between the particles and the polymer chain occur inevitably, which further affects the mechanical properties of the material. This study investigated the effect of temperature on magnetorheological hysteresis properties and its mechanism by employing a large-amplitude-oscillation-shear test method at different temperatures (i.e., 10 °C, 30 °C, 50 °C, 70 °C, 90 °C). The temperature behavior of the MR gel-70 is experimentally evaluated under various loading conditions, including five levels of current inputs of 0 A, 0.5 A, 1 A, 2 A and 4 A, and three excitation frequencies of 5 Hz, 10 Hz and 15 Hz, respectively. The microstructure and the magnetic performance of the sample are probed by employing a scanning electron microscope and vibrating sample magnetometer. It is indicated from the result that magnetorheological gel as a magnetized-induced material and its mechanical properties are greatly influenced by temperature, current and frequency.

It is of great significance to explore the mechanism of temperature influence on magnetorheological gel before employing materials for device design.

Magneto-induced rheological properties of magnetorheological gel under quasi-static shear with large deformation

Magnetorheological gel (MRG) is a kind of magneto-sensitive smart material mainly composed of soft magnetic particles and polyurethane, which can decrease or even avoid the severe sedimentation problem appearing in MR fluids. In this work, the rheological properties of MRG under quasi-statically monotonic and cyclic loading with large deformation were investigated, respectively. The results could provide effective guidance for the design of MR devices that are often subjected to quasi-static loading. Firstly, MRG was fabricated by mixing carbonyl iron particles (CIPs) with the polyurethane matrix. Then, variations of normal force with time and magnetic field for MRG were tested and discussed. Moreover, the influences of CIPs content, shear rate, shear strain amplitude and magnetic field on the energy dissipation density of MRG were analyzed. The results showed the magneto-induced damping performance of MRG is highly relevant to the CIPs content and magnetic field, i.e. the magneto-induced enhancement of energy dissipation density of MRG with 60% CIPs content could reach up to 104 900% when the external magnetic strength increases to 391 kA m⁻¹. Furthermore, the related mechanisms, from the perspective of microstructure, were proposed to qualitatively explain the various mechanical phenomena occurring in shear stress and normal force.

Magnetorheological gel is a material composed of magnetic particles and polyurethane. CIPs content, shear rate, shear strain amplitude and magnetic field affect damping performance. The magento-induced enhancement of energy dissipation density of MRG-60 could reach 104900%.