Magnetorheological fluids (MRFs) can change their viscosity in response to applied magnetic field. Magnetorheological energy absorbers (MREAs) are being investigated for adaptive shock isolation because MREAs can adjust their stroking load to severity of impact when magnetic field is used to control MRF viscosity. Employing MRFs in MREAs requires a highly stable suspension to maintain a uniform concentration, because MREAs would be used only in the event of an impact or crash event, that is, rarely. Suspension stability of MRFs can be studied using an automated vertical axis inductance monitoring system (AVAIMS), where an inductance sensor is translated vertically along a column of MRF to measure particle concentration as a function of column height and time [1,2]. The AVAIMS allows for tracking discontinuities in density or shocks including: the mud-line (boundary between the topmost supernatant (clear fluid) zone and the original concentration zone), the gel-line (boundary between the original concentration zone below mud-line and variable concentration zone), and the cake-line (boundary between the variable concentration zone and the sediment zone at the bottom of the column). MRF sedimentation can be evaluated comprehensively analyzing these boundaries. The AVAIMS developed here (Fig. 1) seeks to improve sedimentation zone boundary localization using an optimized inductance sensor to measure concentration gradient as a function of time. The inductance sensor design, material selection, and geometry were optimized and permalloy and plastic were used advantageously to improve sensor sensitivity. The calibration curve of the sensor was obtained by measuring samples with different particle volume fractions. The sensor design was validated by examining a uniformly mixed MRF column for seven consecutive days after preparation of an MRF with an Fe solids loading of 20 vol%. These tests show that the AVAIMS developed here was able to better localize sedimentation zone boundaries using concentration gradient profile method (Fig. 2).

Sedimentation of Magnetorheological Fluids Measured Using a Automated Vertical Axis Inductance Monitoring System

Magnetorheological fluids (MRFs) consist of micron-sized magnetic particles dispersed in a carrier fluid for which rheological properties can be tuned reversibly with
magnetic field.1 If an MRF is contained in a cellular elastomeric encapsulant (CEE), its mechanical properties, such as stiffness and damping, can be controlled via magnetic field. Such
tunability can be exploited for adaptive vibration control or energy absorption systems. A magnetorheological damper often uses an accumulator to modulate pressure injected by external
forces applied to the damper.2 An accumulator is implemented into the cellular encapsulant to enable essentially incompressible fluid to enter the accumulator and to allow compression of
the cellular material to take place, and also enables a mechanical bulge stiffness to the design.
Here, MRF was prepared with silicon oil (40% vol. fraction). Thermoplastic polyurethane (TPU) was 3-D printed as the CEE system. (Fig. 1 a). The MRF was injected into the TPU-CEE,
followed by the printing of a sealing layer. The wall adjacent to the sealing layer had a circular opening and a TPU membrane was bonded to its perimeter so that the pressurized MRF
could flow through the opening and be accumulated in the resulting pocket.
An external magnetic field (0 and 7 kG) was applied along the sample longitudinal axis at the time of uniaxial dynamic testing with 5% pre-strain. The TPU-CEE samples were
characterized via force-displacement tests at 1 Hz under strain amplitudes. The MR effect on the dynamic stiffness is defined as the ratio of the dynamic stiffness under the maximum
magnetic field to the dynamic stiffness in the absence of a magnetic field. Dynamic stiffness in the presence as opposed to the absence of magnetic field was 264%. (Fig.2a) The area of the
force-displacement curve of the system with an accumulator is about 41% greater than one without an accumulator. The accumulator enhanced the increase in damping (Fig. 2b). The
increase in damping capacity generally increased as strain amplitude increased. 

**References:** 

1. Ashtiani M, Hashemabadi SH, Ghaffari A. A review on the magnetorheological fluid preparation and stabilization. Journal of Magnetism and Magnetic Materials. 374, 716.
(2015) 
2. Yu, Jianqiang & Dong, Xiaomin & Wang, Xuhong & Pan, Chengwang & Zhou, Yaqin. Asymmetric Dynamic Model of Temperature-Dependent Magnetorheological Damper and
Application for Semi-active System. Frontiers in Materials. 6. 227. (2019) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/9e96476131d9b4e1a0c5d4b36a289cf6.png)

Development of Magnetorheological Fluids within 3D Printed Elastomeric Cellular Structures with an Accumulator

An effective vibration isolator (VI) strategy isolates payloads from vibration sources by introducing compliance. Passive isolators are low cost and easy to install but are
tuned to a specific vibration spectrum, and rapidly lose effectiveness if the design point shifts. In contrast, adaptive vibration isolators using magnetorheological fluids (MRFs) continuously
adapt to changing vibration spectra by adjusting a magnetic field using an appropriate control algorithm. Traditional fabrication methods using injection molding are economical only when
large numbers are produced, which precludes customizing VIs for a specific available jitter space, natural frequency, or static displacement. 3D printing is advantageous for a
magnetorheological vibration isolator (MRVI) because designs can be customized: the shape of the hydraulic rubber reservoir can be economically customized to meet the requirements of
a specific application by tuning such properties as axial stiffness, bulge stiffness, diameter, height, and Shore hardness of the membrane wall. The MRVI, which is a squeeze-mode device,
consists of a reservoir or rubber bellow with customizable stiffnesses, a plastic lid which houses an electromagnetic coil, and an MRF (Figure 1). The rubber bellow and plastic lid were
fabricated using a Masked Stereolithography (MSLA) 3D printer. The electromagnet was mounted onto the lid, the reservoir was filled with an MRF, and the lid was twisted onto the
reservoir using a large thread. Using a testing machine, the damper forces of the 3D-printed MRVI were measured under constant velocity conditions for different magnetic fields. From
these tests, the magnetic field-controllable performances such as the dissipated energy and the dynamic force range of the MRVI were obtained (Figure 2). The feasibility of the 3D-printed
MRVI was experimentally confirmed. In addition, using 3D printing, and by selecting Shore hardness of the material, wall thickness, bellow shape, and MRF Fe particle volume fraction, a
broad range of VI applications can be addressed with this design methodology. 

**References:** 

1. S. Kaul, “Modeling and Analysis of Passive Vibration Isolation Systems,” Elsevier, 1st Ed., 2021, DOI: 10.1016/C2019-0-00013-1. 
2. M. Brigley, Y. T. Choi and N. M. Wereley, “Experimental and Theoretical Development of Multiple Fluid Mode Magnetorheological Isolators,” Journal of Guidance, Control, and
Dynamics, Vol. 31, No. 3, pp. 449-459, 2008, DOI: 10.2514/1.32969. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/5c7c2045710ce341660d7efb86aa0b91.png)

Design and Performance of A 3D Printed Magnetorheological Fluid

Magnetorheological fluid (MRF) is a magnetic particle reinforced fluidic material, which is mechanical properties, such as stiffness and damping, can be controlled with the application of a magnetic field.1 Smart sensor and actuator can be fabricated for adaptive vibration control systems where mechanical properties can be controlled by the application of a magnetic field. Manufacturability of MR fluid systems using the additive manufacturing (AM) process has gained great attention to enable the geometrical design of the MR fluid in an elastic component.2 In this research, MR fluid was prepared by carbonyl irons which are 6 – 10 μm in diameter with silicon oil (40% volume fraction). Thermoplastic polyurethane (TPU) with shore hardness 60A was used as an elastomeric system. A 3D printer is used to produce cylindrical TPU elastomer with grid structure using 50 % infill (Figure 1a). The MR fluid was added into the TPU elastomer, followed by adding a sealing layer with 3D printing. An external magnetic field (0 and 7 kG) was applied along the sample longitudinal axis at the time of uniaxial dynamic testing with 10% pre-strain. The TPU-MRF samples were characterized via force-displacement tests conducted at 1 Hz under strain amplitudes of 2%. The MR effect on the dynamic stiffness is defined as the ratio of the dynamic stiffness under the maximum magnetic field to the dynamic stiffness in the absence of a magnetic field. Mechanical testing results with the magnetic fields show that the MR effect on the dynamic stiffness is 1.65. (Figure 2a). The area of the force-displacement curve at 7 kG is about 6.5 times larger than the result with 0 kG, indicating a significantly large change in damping property. Frequency was varied from 1 to 10 Hz and the force-displacement curve didn’t show significant changes, indicating that the performance of the TPU-MRF system doesn’t diminish with increased frequency. (Figure 2b)

![](https://assets.underline.io/uploads/markdown_image/1/image/19adad7fc103540f67a0f0d92653914f.jpg)

Figure 1 (a) Schematic diagram of a TPU-MRF sample fabrication (b) Image of TPU grid structure, TPU sample with and without MR fluid.

![](https://assets.underline.io/uploads/markdown_image/1/image/38dc14fab1586b1c5bfaea4cfc340707.jpg)

Figure 2 (a) Force-displacement curve of TPU-MRF with 0 and 7 kG. (2% strain) (b) Force-displacement curves of TPU-MRF with a different frequency of vibration at 7 kG. (3% strain)

Encapsulations of Magnetorheological Fluids using 3D Printed Elastomeric Rectangular Cellular Structures

Smart materials can change key physical properties in response to external stimuli. To achieve adaptive design performance regardless of environmental changes, demand for smart materials technology has greatly increased. Magnetorheological (MR) composites are a class of smart materials that can rapidly and reversibly control adjust their damping and stiffness properties in response to external magnetic field. MR composites consist of micron-size soft magnetic particles in a non-magnetic carrier matrix. MR composites can be divided into three major classes based on matrix materials: MR fluids (MRFs), MR foams, and MR elastomers (MREs). The rheological properties of MRFs, which use liquid as the carrier matrix, can be controlled in response to an external magnetic field. MRFs have been widely applied to a variety of hydraulic actuators to produce a controllable damper force or torque. MR foams are composed of either non-magnetic porous metal foam filled with MRF or have particles embedded in a porous elastomeric foam. Because of their light weight and high compliance, MR foams exhibit large changes in baseline stiffness and are candidate smart materials for space applications, as well as vibration and acoustic absorption applications. MREs, which use a non-porous solid elastomer as the carrier matrix, have controllable viscoelastic properties. MREs can used to retrofit passive rubber isolators and mounts in vibration and shock mitigation systems to provide improved and adaptive performance. MRFs typically exhibit sedimentation because of the large density difference between carbonyl Fe particles (density of 7.9 g/ml) and the non-magnetic carrier fluid (e.g., silicone oil has a density of 0.97 g/ml). Unlike MRFs, the Fe particles in MR foams and MREs are permanently dispersed. Because particles are embedded in the carrier matrix, MR foams and MREs show less MR effect than MRFs where particles can migrate and agglomerate. To increase MR effects in MREs, research [1-4] to encapsulate MRFs in MREs has been reported. It should be noted that MR foams have porous carrier matrix and may be not possible to encapsulate MRF into MR foam. In this study, MRF encapsulated elastomers (MREEs) are fabricated and their controllable stress behaviors are experimentally evaluated. Two design configurations are studied for MREEs: the first is MRF and permanent magnet (PM) embedded inside MREEs, and the second is MRF only embedded in MREEs. MREEs with PM can be passively and actively activated, but MREEs without PM can be only activated by external magnetic field produced by an electromagnet. A sample MREE (Figure 1) encapsulates an MRF composed of 35 vol% carbonyl Fe dispersed in a 1,000 cSt silicone oil. The silicone rubber was as soft as 00-20. The diameter and height of this sample was nominally 2.6” and 0.37”, respectively. The compressive stress-strain curve of the MREEs both without and with applied magnetic field were measured by a MTS machine. Figure 2 presents the measured field-dependent compressive stress curves of the MREE. As seen in this figure, the compressive stress curves of the MREE can be continuously adjusted in response to current input. Also, the hysteresis loop also increased as the applied current inputs. This physically implies that the dissipated energy increased. In the full paper, the effect of two different magnetic flux directions (i.e., positive and negative coil currents) will be presented. The compressive stress curve of the MREEs can also be affected by the strain rate, as in impact events. To illustrate such strain rate effects, the compressive stress curves over a range of strain rates will be also presented. From the measured hysteresis loop, the dissipated energy can also determined. In addition, the MREEs can be stacked for accommodating larger compressive displacement. In this study, the effect of two different stackable situations (one is attractive PMs configuration and the other is repulsive PMs configuration) on the compressive stress curve will be evaluated. From the results presented in this study, the controllable stress capability of the MREEs will be presented for a range of operating conditions.

**References:**

[1] D. York, X. Wang, and F. Gordaninejad, “A new MR fluid-elastomer vibration isolator,” J. Intel. Mater. Syst. and Struct, 18: 1221-1225 (2007). [2] D. York, X. Wang, F. Gordnaniejad, “A new magnetorheological mount for vibration control,” J. Vibr Acoust., 133: 031003 (2011). [3] A. K. Bastola, L. Li and M. Paudel, |A hybrid magnetorheological elastomer developed by encapsulation of magnetorheological fluid,” Journal of Materials Science, Vol. 53, pp. 7004-7016 (2018). [4] A. K. Bastola, E. Ang, M. Paudel, L. Li, “Soft hybrid magnetorheological elastomer: gap bridging between MR fluid and MR elastomer,” Colloids and Surfaces A, Vol. 583, 123975 (2019).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/c7b4531d44116ed3566e15610b99a51e.jpg)
Figure 1. MRF encapsulated elastomers (MREEs).

![](https://assets.underline.io/uploads/markdown_image/1/image/84dd4f6d08b64d7a6a8dcdde1ea3c75f.jpg)
Figure 2. Field-dependent compressive stress curves of the MREE.

 Controllable Stress of Magnetorheological Fluid Encapsulated Elastomers

Magnetorheological elastomer (MRE) is a magnetic particle reinforced elastomer composite, which its mechanical properties can be controlled with the application of a magnetic field.1 The magnetorheological effect induces changes in stiffness and damping properties in the composite with the response of the magnetic particles to the external magnetic field.2 Smart sensor and actuator components can be fabricated for adaptive vibration control systems where mechanical properties can be controlled by the application of magnetic field. Typically, composites are prepared by mixing magnetic particles with the uncured rubber matrix and then the mixture is poured into a mold for curing. Recently low-cost 3D printers are widely available, utilizing various polymers. Manufacturability of MRE composites using additive manufacturing (AM) process has gained great attention so the geometrical design of the MRE composite fabrication can be achieved.3 In this research, development of filament of MRE for fused filament fabrication based on additive manufacturing is performed. The magnetorheological effect depends on the particle’s magnetic properties and volume fraction, and distribution, etc. Filament materials are developed by mixing thermoplastic polyurethane (TPU) pellets with the magnetic particles (iron oxide, carbonyl Fe particles), followed by extrusion process to produce rolls of filament. Due to the nature of the mixing process relying on gravity to feed material into the extruder, denser and much smaller magnetic particles (~10 μm) than the TPU pellets (~mm) tend to fall to the bottom of the hopper, leading non-uniform distribution of magnetic particle along the filament thru extrusion process. Therefore, the trickling systems with a screw feeder were developed to provide consistent trickling rate of each TPU and magnetic particles respectability. [Figure 1 (a)] The trickling rate of TPU was fixed at ~4.9 g/min and the trickling rate of iron oxide was varied from 0.0 to 2.5 g/min. Five sets of filaments were produced with different trickling rates of iron oxide.[Figure 1(b)]. Diameter ranges from 1.45 ± 0.01 to 1.55 ± 0.06 mm. The density of filament increases with the higher trickling rate of magnetic powder and the densities change from 1.33 ± 0.05 to 1.46 ± 0.05 g/cc, indicating that the volume fraction control of magnetic particles in the extrusion process was successful. The grayscale level plot [Figure 1 (c)] indicates the iron oxide concentration in each filament in the yellow box region. The grayscale plot profiles the images with each point represents the average pixel intensity. This data shows that the filaments produced with lower trickling rate (0.6 and 1.0 g/min) did not show significant difference but the lower gray scale values of filaments with 1.5 and 2.5 g/min indicate that there are more iron oxide particles. Micro-focus X-ray tomography scans were performed on the produced composite filament (Figure 2). The results show that magnetic particles are well dispersed in the matrix. The small grains are &lt; ~30 mm and the larger grains are ~60 mm. The iron oxide volume fraction ranges from 9.31% to 12.95%. This demonstrates that MRE filament feedstock materials can be successfully manufactured for use in fused filament deposition processes.

**References:**

1. S. S. Kang, K. Choi, and J. D. Nam, Materials., Vol.13, p.4597 (2020) 2. O. Padalka, H. J. Song, N. M. Wereley, J. A. Filer, IEEE Transactions on Magnetics, Vol. 46, p.2275 (2010) 3. A. K. Bastola, M. Paudel, L. Li, Smart Materials and Structures, Vol. 29, p.123002 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/b3aba021d44c39dfd0f2da3a1c22aa82.jpg)
Figure 1 (a) Schematic drawing and image of developed trickling system. (b) coils of TPU filaments produced with different amount of iron oxide. (c) image of extruded filaments and plot profile of the yellow box.

![](https://assets.underline.io/uploads/markdown_image/1/image/f2f413611412f4c079a9eb2b2e621762.jpg)
Figure 2 X-ray tomography scan performed on the produced composite filament. Iron oxide particles are highlighted with color coding by volume. The TPU matrix is colored in light gray to easily visualize the pores and iron oxide dispersions.

 Magnetic Particle Reinforced Elastomer Composites for Additive Manufacturing

Aircraft propellers are a constant source producing excessive vibrations and noise due to aerodynamic loads imposed in flight. Such vibrations are transmitted to the cockpit and aircrews are inevitably exposed to the high levels of vibrations during flight. The prolonged exposure to severe vibrations due to extended missions can cause the discomfort and fatigue of the occupants, reducing the ability to make correct judgement and appropriate actions during the flight. One of effective way to provide comfortable work environment to occupants is to design a seat equipped with vibration absorbers that can isolate or reduce the unwanted vibration transmitted from the cockpit floor to occupant body. In this study, the adaptively tunable magnetorheological elastomer (MRE)-based vibration absorber was proposed for achieving better vibration reduction performance of a propeller aircraft seat. Since MREs are one of smart materials that can change their key physical properties by external stimuli, MRE-based vibration absorbers can provide both variable stiffness and damping by adjusting the magnetic field. As a result, MRE-based vibration absorbers have an adaptively tunable capability working at wider frequency range that can overcome the narrow operating frequency limitation of passive vibration absorbers. In this study, the simple but effective design of the MRE-based vibration absorber for a propeller aircraft seat was presented (Figure 1). In order to effectively concentrate the magnetic field generated from the electromagnet into the MRE pad areas, the electromagnetic analysis was also conducted by using a finite element method. Based on this analysis, the MRE-based vibration absorber was fabricated. The damper force characteristics of the MRE-based vibration absorber was experimentally evaluated by using an Instron material testing device. In order to confirm the tunability of the MRE-based vibration absorber, the frequency responses with respect to applied current inputs was experimentally obtained (Figure 2).

![](https://assets.underline.io/uploads/markdown_image/1/image/916bf925ae3a3874b07730e6331d4772.jpg)

Figure 1. MRE-based vibration absorber for a propeller aircraft seat

![](https://assets.underline.io/uploads/markdown_image/1/image/4ece2ead9c2a1228811bea21fba1ab33.jpg)

Figure 2. Frequency responses of the MRE-based vibration absorber

Adaptively Tunable Magnetorheological Elastomer-Based Vibration Absorber for a Propeller Aircraft Seat

QOB: Magnetic Stimulation in Biology, Magnetic Fluids and Actuators

technical paper

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

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QPB: Manipulation of Magnetic Fluids

poster

**Session chairs:** Manh-Huong Phan, University of South Florida and Jungjin Park, University of Maryland at College Park


IOI - Magnetic Fluids, Antibacterial Applications, and Other Emerging Topics

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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YB: Focus Session: Magnetorheological Composite Materials and Applications

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Norman Wereley

7

7

SHORT BIO

Presentations

Sedimentation of Magnetorheological Fluids Measured Using a Automated Vertical Axis Inductance Monitoring System

Development of Magnetorheological Fluids within 3D Printed Elastomeric Cellular Structures with an Accumulator

Design and Performance of A 3D Printed Magnetorheological Fluid

Encapsulations of Magnetorheological Fluids using 3D Printed Elastomeric Rectangular Cellular Structures

Controllable Stress of Magnetorheological Fluid Encapsulated Elastomers

Magnetic Particle Reinforced Elastomer Composites for Additive Manufacturing

Adaptively Tunable Magnetorheological Elastomer-Based Vibration Absorber for a Propeller Aircraft Seat

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