Magnetorheological Foam Research Articles

Thermo-rheological improvement of magnetorheological foam with the addition of silica nanoparticles

Magnetorheological (MR) foam has become a potential soft robotic gripper-based material that can provide a better grasping force and handling objects due to its ability in varying stiffness in correspond to applied magnetic fields. However, MR foams are facing degradation issue that may reduce the storage modulus when often exposed to thermal exposure from the operating system of a device. Therefore, this study focuses on improving the storage modulus and simultaneously enhancing the thermal properties of MR foam. Hence, silica nanoparticles were introduced as an additive to achieve the improvement target. MR foams were embedded with different concentrations of silica nanoparticles from 0 to 5 wt.%, and the corresponding rheological properties was examined under different temperature conditions from 25 °C to 65 °C. The results revealed that increasing temperatures have reduced the storage modulus of MR foams, however, the embedded silica has countered the drawbacks by strengthening the interfacial interactions between CIP-polyurethane foam matrix. In addition, the morphological characteristics of MR foams also showed less debris or peel-off PU foam with silica nanoparticles. Besides, the silica nanoparticles have delayed the thermal degradation of MR foam for approximately 30 °C.

Enhancement of the rheological properties of magnetorheological foam via different constraint volumes foaming approach

The potential of magnetorheological (MR) foam, a recently developed porous smart material, has grown rapidly in recent years. The ability of MR foam to change its properties continuously, actively, and reversibly in response to a controlled external magnetic stimulus is one of its advantages for applications in advanced technology industries. However, its ability to store energy is still relatively low. This study attempts to address this drawback by highlighting a method to improve this ability by enhancing the material's storage modulus by introducing constrained foaming during the fabrication process. MR foam containing 75 wt% carbonyl iron particles (CIPs) was prepared in situ using two foaming approaches: free and constrained foaming. The effect of constraint foaming on the storage modulus enhancement was further investigated by reducing the mold length by 25 % and 50 %. The rheological properties of the fabricated MR foam samples were then examined using a rheometer in both the absence and presence of magnetic fields in an oscillatory shear mode. Thus, this study showed that constraint foaming has successfully improved the properties, especially regarding storage modulus and MR effect. When the mold volume was further reduced by 50 %, the storage modulus increased by about 50 % compared to a free-foaming MR foam at off-state conditions. Meanwhile, the results portrayed a higher storage modulus value under a 0.659 T magnetic field. This positive enhancement was believed to be due to a more compact CIP distribution. Hence, constraint volume MR foams were able to form stronger chain-like structures. The micrograph analysis by digital microscope revealed that the pore size decreased as the mold length was reduced. A shorter mold resulted in a more compact distribution of magnetic particles. As a result, MR foam with constrained foaming, especially at 50 % mold length, has a higher storage modulus. Overall, using constrained foaming to fabricate MR foam could improve the structure and mechanical properties of MR foam for a wide range of smart devices.

Preparation and magneto-mechanical properties of 3D microporous magnetorheological foam

Magnetorheological (MR) materials with excellent magneto-mechanical properties have great application values in the field of vibration reduction and buffering. By combining the advantages of light weight and excellent energy absorption of porous polymer materials, the development of porous MR materials can improve the buffer performance of MR technology. In this paper, we proposed a one-step method for fabricating the 3D microporous MR foam based on polyurethane matrix. Micromorphology of MR foam character by scanning electron microscope shows the existence of a 3D network structure with embedded carbonyl iron particles (CIPs). The unique 3D microporous structure ensures the excellent magneto-mechanical properties of MR foam. The test results analyzed by a rheometer reveal that its compressive modulus and shear storage modulus enhanced significantly with the magnetic field. The influence factors such as CIP content, shear frequency, and shear strain have been systematically studied under the oscillating shear mode. It indicated that the MR foam exhibits obvious viscoelasticity, the dynamic modulus depends on the shear frequency and shear strain, and it has excellent magneto-mechanical properties. This work can provide a new technical solution for fabrication of MR porous materials for MR buffer technology.

Bibliometric Review of Magnetorheological Materials

The findings and technological developments related to intelligent materials are increasingly attracting the attention of scientists. One such field is that of magnetorheological (MR) materials. Scientific studies on MR materials have been carried out to determine the performance and characteristics of, for example, MR dampers, MR elastomers, and MR foams. To the best of the authors’ knowledge, there has been no statistical discussion in the form of bibliometric analyses of developments in the field of MR materials in the last ten years. This is fascinating, considering that bibliometric studies have considerable impacts and contributions, such as studies on the growth of research patterns, avoiding the repetition of research topics, and analyzing future research. This also supports the future sustainability of the topic of MR materials, helping to bridge the gap that has probably existed since the introduction of MR materials. The relationship between the authors’ scientific research, domestic and global collaborations, and the evolution of themes over the last few years is also shown in this analysis. Thus, this study aimed to fill the gap in such materials by conducting a bibliometric analysis of 1830 articles related to MR materials published over the last 10 years. The results indicated that the field of MR materials has exhibited good growth. The introduction of MR fluid materials to new types of MR materials is still in the early stages of research, such as in applications with MR foam. Further analysis showed that there is a connection and dominance of scientific publications related to MR technology. Furthermore, based on bibliometric analysis, dominant theme changes in the area of MR elastomers, particularly related to carbonyl iron particles and MR polishing, is seldom mentioned, as is also the case for MR gels, MR foam, and MR grease. However, the discussion of new MR materials is a good opportunity to promote developments in the field of MR materials.

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.

Magnetic and Tunable Sound Absorption Properties of an In-Situ Prepared Magnetorheological Foam.

Conventional polyurethane foam has non-tunable sound absorption properties. Here, a magneto-induced foam, called magnetorheological (MR) foam, was fabricated with the feature of being able to tune sound absorption properties, primarily from the middle- to higher-frequency ranges. Three different samples of MR foams were fabricated in situ by varying the concentration of Carbonyl Iron Particles (CIPs) (0, 35, and 75 wt.%). The magnetization properties and tunable sound absorption characteristics were evaluated. From the magnetic saturation properties, the results showed very narrow and small coercivity of hysteresis loops relative to the soft magnetic properties of the CIPs. MR foam with 75 wt.% CIPs showed a higher magnetic saturation at 91.350 emu/g compared to MR foam with 35 wt.% CIPs at 63.896 emu/g. For tunable sound absorption testing, the effect of ‘shifting’ to higher frequency was also observed when the magnetic field was applied, which was ~10 Hz for MR foam with 35 wt.% CIPs and ~130 Hz for MR foam with 75 wt.% CIPs. As the latest evolution of semi-active noise control materials, the results from this study are valuable guidance for the advancement of MR-based devices.

Relationship between the response of microscopic and magnetic properties with highly uniform dispersion of carbonyl iron particles in magnetorheological polyurethane foam

Magnetorheological (MR) foam, which is comprised of magnetic particles inside the matrix phase, is capable of changing its physical and rheological properties corresponding to the applied magnetic field. However, the performance of this material seems unsatisfactory due to the nonuniform distribution of magnetic particles throughout the composite area resulting in uneven magnetic properties. Since uniform magnetic properties are significant regarding MR foam, in situ fabrication using a polyvinyl chloride mould can be used to achieve the targetted improvement. MR foam was prepared with various amounts of carbonyl iron particles (CIPs), 0, 35, 45 and 55 wt%, and investigated at three different positions (top, middle and bottom parts) with a vibration sample magnetometer. The results showed that the hysteresis loop at all CIP concentrations of 35, 45 and 55 wt% exhibited superparamagnetic properties with magnetic saturation. The M s of the top, middle and bottom positions were almost the same with a small standard deviation below 2 Am2 kg–1. Moreover, it is observed that the effect of porosity results in the enhancement of the magnetic saturation and remanence values. These results reveal the promising uniform magnetic properties of MR foam, which can benefit the industry by helping produce a consistent MR foam.

Characterization of morphological and rheological properties of rigid magnetorheological foams via in situ fabrication method

This paper presents material characteristics of a rigid magnetorheological (MR) foam that comprises polyurethane foam matrix and carbonyl iron particles (CIPs). Three different samples of MR foams are prepared by changing the concentration of CIPs (0, 35, and 70 g) in isotropic condition. In-depth characterization on the morphological properties, the field-dependent rheological behavior in terms of linear viscoelastic region and storage modulus, and the off-state sound absorption properties are then experimentally investigated. In the morphological observation, it is seen from the fluorescence micrographs that MR foam consists of open pore structure and the average size of the pores is decreased with the increment in CIPs content. In the rheological test of MR foam, it is identified that MR foam with the addition of 70 g of CIPs to the total of polyol and isocyanates (100 g) can enhance the storage modulus up to 112% compared with MR foam without CIPs. In the meantime, from the acoustic absorption test, it is shown that the maximum peaks of sound absorption coefficient (SAC) are shifted to the low frequency and the SAC is increased up to 229% due to the decrement in the pores size and increment in the storage modulus. The results achieved from this material characterization of MR foam provide useful guidelines for the development of new type smart materials associated with MR fluids and for the findings of appropriate applications which require controllability of both the stiffness and acoustic properties.

Smart polyurethane foam with magnetic field controlled modulus and anisotropic compression property

A new kind of polyurethane (PU) magnetorheological (MR) foam was prepared via in situ polymerization and foaming for the first time. A chain-like structure of carbonyl iron particles in the liquid polyol is formed after orientation at a magnetic field and fixed in the PU foam after the in situ curing. The anisotropic PU MR foam possesses an anisotropic compression property. The compression strength along the magnetic chain direction reaches ∼1053.5 KPa for the sample with 80 wt% carbonyl iron content, which is ∼878 times that of the blank foam and ∼57 times of that at the vertical direction of the same sample. The PU MR foam exhibits a magnetic field controlled shear modulus, i.e., MR effect, which can be adjusted by changing the orientation structure and content of the carbonyl iron, test frequency and magnetic field strength. The maximum absolute and relative MR effects for the anisotropic PU MR foam are ∼1.07 MPa and ∼27.1%, respectively. Moreover, the introduction of carbonyl iron particles can notably improve the acoustic absorption properties in the low frequency region.

Magnetorheological Elastomer：State and Application

Magnetorheological(MR) materials, which consist of magnetic particles in a non-magnetic medium can be divided into three kinds: MR fluid, MR foam and MR elastomer (MRE),MRE is a new branch of MR materials whose mechanical property can be changed quickly and reversibly by the application of an external magnetic field[1]. In this paper, the new research, typical modeling and various experiments will be reviewed and discussed. So far MREs have been used in tons of scientific filed owing to their significant advantages and MREs will have more promising applications.

Vibration Mitigation Using Passive Active Tunable (PAT) System: Experimental Aspects

The objective of this paper is to test and model a single-degree-of-freedom vibration isolation system with a magnetorheological (MR) foam damper under harmonic and random excitations. The results of this research are valuable for understanding the characteristics of the MR foam damper and include the experimental design and results of vibration mitigations for frequency ranges up to 2000Hz. Transmissibility and acceleration hysteresis experiments of the MR foam damper system with different levels of input current are discussed. A simple damper design that eliminates many of the constraints normally associated with fluid filled devices is presented. Constitutive equations of the Bouc–Wen model are used to validate and characterize the MR foam damper. The motion characteristics of the MR foam damper are studied. Experimental results reveal that the mechanical behavior of the MR foam damper is nonlinear and that the field-dependent behavior of MR foam damper is associated with the applied frequency and acceleration amplitude. Experiments demonstrate MR foam damper works well in controlling vibrations and can be controlled and tuned for specific applications.

MR fluid, foam and elastomer devices

Magnetorheological (MR) fluids, foams and elastomers comprise a class of smart materials whose rheological properties may be controlled by the application of an external magnetic field. MR fluids are liquids whose flow or shear properties are easily controlled to enable a variety of unique torque transfer or vibration control devices. MR foams, in which the controllable fluid is contained in an absorptive matrix, provide a convenient way of realizing the benefits of MR fluids in highly cost sensitive applications. MR elastomers are solid, rubber-like materials whose stiffness may be controlled to provide tunable or adjustable mounts and suspension devices.