Development and validation of a lateral MREs isolator Zhi-Wei Xinga, Miao Yu*a, Jie Fua, Lu-Jie Zhaoa

a Key Laboratory for Optoelectronic Technology and Systems of Ministry of Education, College ofOptoelectronic Engineering, Chongqing University, Chongqing, China 400044

ABSTRACT

A novel lateral vibration isolator utilizing magnetorheological elastomers (MREs) with the field-dependent damping and stiffness was proposed in order to improve the adaptive performance. First, soft silicone rubber MREs with a highly adjustable shear storage modulus was fabricated. Then, the lateral MREs isolator was developed with a unique laminated structure of MRE layers and steel plates, which enables to withstand large vertical loads and adapts to the situation of large lateral displacement. Also, the electromagnetic analysis and design employed electromagnetic finite element method (FEM) to optimize magnetic circuit inside the proposed device. To evaluate the effectiveness of the lateral MREs isolator, a series of experimental tests were carried out under various applied magnetic fields. Experimental results show that the proposed MREs isolator can triumphantly change the lateral stiffness and equivalent damping up to 140% and 125%, respectively. This work demonstrates the performance of the designed lateral MREs isolator and its capacity in vibration mitigation for the complex situation.

Keywords: Magnetorheological elastomers, finite element method, isolator, vibration mitigation

1. INTRODUCTIONLateral base isolators have been widely employed in the manufacture procedure of semiconductors and opticalcomponents to guarantee the quality of ultra-precision products for the high-tech equipment, due to the requirements of a restrictive environment with extremely limited vibration. The main objective of using the base isolator is to reduce theinertia force transmitted into the superstructures so as to avoid related damage phenomena1. However, due to the passivenature of existing lateral base isolators, once the base isolation system has been designed and installed, it cannot change the performance of structures against different types of vibrations. To overcome this challenge, it is extremely desired to develop a smart lateral base isolator which enables to withstand large vertical loads while possessing controllable lateral stiffness. In addition, variable damping and stiffness isolators are prepared to avoid resonant response during complexexcitation motions by altering the properties of the structure.

Magnetorheological elastomers (MREs) have the potential to be adopted as semi-active controllable elements in base isolation, because their damping and stiffness change when subjected to an external magnetic field. MREs are solid analogous to magnetorheological fluids (MRFs), with micron-sized magnetic ferromagnetic particles dispersed in a polymer matrix2-4. Due to the advantages of no-sedimentation of particles in certain matrix, fast response, and wide rangeof operation frequency, a great deal of efforts have been made by investigators and researchers in recent years to employing MREs to design smart adaptive absorbers or isolators, such as adaptive tuned vibration absorber5, real-time tunable stiffness and damping mount6, vehicle seat suspension isolator7, seismic base isolator8,9, variable stiffness and damping isolator (VSDI)10. All of the above MREs devices have achieved controllable performance under externalapplied electric current.

In this paper, we explore the feasibility of a novel lateral MREs isolator incorporating MREs materials. The adjustable base isolator is then fabricated utilizing a traditional laminated bearing structure. Also, the electromagnetic analysis employed electromagnetic finite element method (FEM) to optimize magnetic circuit inside the proposed device. Comprehensive experimental testing was conducted to evaluate the performance of the proposed lateral MREs isolator.

*yumiao@cqu.edu.cn; phone 86 23 65111016; fax 86 23 65111016

Ninth International Symposium on Precision Engineering Measurement and Instrumentation edited by Jiubin Tan, Xianfang Wen Proc. of SPIE Vol. 9446, 944645 · © 2015 SPIE

CCC code: 0277-786X/15/$18 doi: 10.1117/12.2181830

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2. DESIGNE OF THE LATERAL MRES ISOLATOR 2.1 Soft MRE preparation and testing

The MRE material is mainly composed magnetic particles in an elastic matrix. To prepare MREs, a two-component room temperature vulcanizing (RTV) silicone rubber was selected as the base elastomer materials, while a silicone oil was mixed within the specimen to change the ductility of the rubber base. The filler particles dispersed in the matrix were carbonyl iron particles. In this work, the mass fraction of the carbonyl iron particles ( 50 5~8d mμ= , Type: JCF2-2, Jilin Jien Nickel Industry Co. Ltd., China), silicone rubber (Type: SC-2110, Beijing Sanchen Industrial New Material Co. Ltd., China) and silicone oil (Kinetic viscosity: 500cSt) was 70%, 17% and 13%, respectively. It is noted that the mixture of components within an uniform aluminum mold was degassed in a vacuum drying oven to remove air bubbles, and cured under a magnetic flux density of 600mT for 24h at room temperature. The iron particles within pre-cured MRE mixture take the shape of chainlike structures by exposing to a magnetic field during solidification, so that the MRE specimens are able to achieve better field-dependent mechanical properties.

After the fabrication procedure of MREs, dynamic mechanical properties of MRE specimens were measured by using an advanced commercial rheometer (MCR 301, Anton Paar Co., Austria). Figure 1 shows the shear storage modulus and MR effect of prepared MRE sample in the case of varying strain under magnetic field sweeping from 0~1.2T. Especially, the MR effect is a critical parameter for evaluating MRE performance, and is defined by Equation (1),

( )max 0100MR-effect 0G = % G -G G′× (1)

where maxG′ is the shear storage at magnetic saturation, 0G is the initial modulus. It is noticed that the MR effect of the sample result in 1500% increase when the magnetic field is 1.2T at a strain of 1%. In addition, under the same magnetic field strength, the shear storage modulus, as well as the MR effect, of MRE sample at small strain is more remarkable than that at larger strain. Thus, in the isolator design, a multilayered structure is adopted to gain large lateral displacement while each MRE layer is able to maintain an appropriate smaller strain.

Figure 1. Mechanical properties of the prepared MRE sample under different magnetic fields.

2.2 Mechanical description

The proposed lateral MREs isolator consists of laminated structure of MRE layers and steel plates, and a solenoid coil, as shown in Figure 2. The laminated structure is conventionally used in the seismic bearing in order to withstand large vertical loads while processing controllable lateral stiffness to achieve higher displacement in the horizontal direction by applying the external magnetic field. In this design, there are 20 layers of MRE sheet with 2mm in thickness and 19 layers of electrical pure iron sheet with 1mm in thickness being adhesive utilizing silicone rubber. In order to generate sufficient magnetic field, the coil winded on a thin non-magnetic bobbin, in which the diameter of the copper wire is 0.8mm and the total electric resistance is 17.2Ω. Moreover, the interval between the laminated structure and the inner wall of the coil cylinder is set to 10mm, which indicate the maximum lateral displacement. To enable the motion of the

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2.6708e +002

1.3381e +002

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isolator, a small gap of 2mm between the sliding surface and steel sleeve is reserved. At last, the other dimensions of parts meet the requirements of assembly design.

Figure 2. Schematic structure of the designed lateral isolator employing MREs.

2.3 Electromagnetic analysis

During the development of this compact prototype isolator, the electromagnetic coil is restricted by the mechanical design. The magnetic field inside the laminated MREs with steel plates is designed and verified by using a two-dimensional electromagnetic finite element analysis (FEA) software package, ANSOFT Maxwell. The magnetic properties of each component are correctly selected and defined in the software. When the applied current is 5 A, the amount of magnetic flux density of the FEA model of the prototype electromagnetic design is presented in Figure 3. According to the result of simulation, it is seemed that the magnetic field intensity reveals a homogeneous distribution about 500mT in the laminated MREs structure.

Figure 3. Result of electromagnetic finite element analysis inside the lateral MREs isolator.

3. PERFORMANCE OF THE LATERAL MRES ISOLATOR 3.1 Experimental setup

With the purpose of evaluating the performance of the proposed lateral MREs isolator, a series of dynamic mechanical tests were carried out. Figure 4 shows the photo of the experimental setup. An electromagnetic vibration shaker with slip table is used to generate harmonic excitations. The mounting plate of the isolator is clamped on the horizontal sliding table without relative displacement, meanwhile the displacement of that sliding table is measured by a laser displacement

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sensor fixed on the ground. The top attached to the load cell is screwed to the fixed support keep still during experiments. A DC supply with a capacity of 10A and 120V provides the various current inputs to energize the electromagnetic coil.

Figure 4. Photo of the experimental setup for lateral MREs isolator.

Each experiment are conducted with a constant frequency including 1Hz, 2Hz and 4Hz, respectively. The amplitudes of the exciting motion were set as 2mm, 4mm and 6mm, respectively. During the test, the lateral MREs isolator was supplied various electric currents at 0-5A with 1A increment. The experimental data including force and displacement is acquired from the load cell and laser displacement sensor. Totally, 54 sets of experimental data were calculated and analyzed via data processing programs.

3.2 Experimental results and discussion

Figure 5 shows a typical force-displacement loops of the propose isolator with a 4mm amplitude at 2Hz under different external currents. Correspondingly, the force-displacement curves under dynamic excitations are demonstrated in Figure 6. It is clearly observed that the isolator exhibits significant force increase with the increase of external electric current.

Figure 5. Force response of the lateral MREs isolator under exciting with X=4mm and f=2Hz.

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50

40

30

20

10

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Displacement/mm1 2

- Current 1 =0A- Current 1 =1A- Current 1 =2A- Current 1 =3A- Current 1 =4A- Current 1 =5A

Figure 6. Force-displacement loops at an amplitude of 4mm and a frequency of 2Hz.

The results also demonstrate that the MR effect has been obviously verified in the designed isolator. For further evaluation of the performance of proposed device, the effective lateral stiffness and equivalent damping are numerically investigated.

Figure 7. Hysteretic damping model and its typical force-displacement loop11.

Referring to the hysteretic damping system, as shown in Figure 7, the effective stiffness is determined by Equation (2) from the force-displacement loops based on the experimental results of the device.

max min

max min

d deff

F FKX X

−=

− (2)

where maxdF and mindF are the positive force at the maximum amplitude maxX and the negative force at the minimum

amplitude minX , respectively. Similarly, the equivalent damping of the lateral MREs isolator, which explores the energy -dissipation performance, can be calculated by:

2 22eqWCfXπ

Δ= (3)

where the area of the force-displacement hysteresis loop gives the damping capacity WΔ , f is the exciting frequency and X is the maximum displacement of the exciting amplitude.

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After summarizing all the experimental data, all the calculated effective stiffness and equivalent damping subjected to various exciting conditions are analyzed, as shown in Table 1 and Table 2, respectively. In Table 1, for the same displacement amplitude and exciting frequency, the lateral effective stiffness increases to varying degrees. While for an exciting amplitude of 2mm at 4Hz, the maximum increase reaches to 140% by applying a current of 5A to the isolator. Comparing the effective stiffness at a same loading frequency, small exciting amplitudes seem to exhibit greater effective stiffness. This is mainly confirmed by the dynamic mechanical properties of MREs material, as shown in Figure 1. It can also be concluded that MREs materials are more suitable for the development of micro-vibration control devices due to remarkable MR effect. However, as a result of the weak initial stiffness of selected MREs samples in this study, it is desired to fabricate high-performance MREs in the future for potential semi-active devices in the field of vibration isolation.

The equivalent damping coefficient indicate the capacity of energy-dissipation in an isolator. According to the results of equivalent damping in Table 2, it is particular evidence that the damping coefficient reveals nearly the same for the same exciting frequency and current value at different displacement amplitude. On the other hand, it is obvious that the equivalent damping coefficient increase with augmented external applied current, but decrease with increasing exciting frequency. In addition, the damping coefficient values at a lower exciting frequency are greater than that under a higher frequency.

Table 1. Lateral effective stiffness of the MRE isolator in different exciting conditions.

effK (kN/m)

X=2mm X=4mm X=6mm 1Hz 2Hz 4Hz 1Hz 2Hz 4Hz 1Hz 2Hz 4Hz

0A 1.3373 3.0992 4.0142 1.4630 3.2035 3.9987 1.8252 3.2991 3.9267

1A 1.5221 3.7580 4.8697 1.5298 3.6409 4.7204 1.8201 3.6731 4.4271

2A 1.8613 4.7849 6.0894 1.7830 4.3111 6.0863 1.9227 4.2770 5.1105

3A 2.2020 5.7117 7.0543 2.0924 5.2824 7.0038 2.1262 4.8748 5.9959

4A 2.5442 6.2755 8.8514 2.4081 5.6781 6.9692 2.2783 5.4407 6.4022

5A 2.9800 7.2285 9.6408 2.6520 6.4579 7.5451 2.3208 6.0622 7.1534

Increase (0~5A)

122.84% 133.24% 140.17% 81.27% 101.59% 88.69% 27.15% 83.75% 82.17%

Table 2. Lateral equivalent damping of the MRE isolator in different exciting conditions.

eqC (kN•s/m)

X=2mm X=4mm X=6mm 1Hz 2Hz 4Hz 1Hz 2Hz 4Hz 1Hz 2Hz 4Hz

0A 0.6878 0.4835 0.1772 0.6704 0.3424 0.1794 0.7136 0.3291 0.1825

1A 0.8425 0.4371 0.2324 0.7881 0.4091 0.2232 0.7832 0.4023 0.2158

2A 1.0734 0.5932 0.3176 0.9779 0.5131 0.2751 0.9153 0.4972 0.2681

3A 1.3069 0.7284 0.3891 1.1764 0.6113 0.3306 1.0646 0.5901 0.3182

4A 1.5317 0.8398 0.4609 1.3367 0.7123 0.3970 1.2006 0.6778 0.3667

5A 1.7277 0.9329 0.5199 1.4649 0.7981 0.4358 1.3066 0.7477 0.4074

Increase (0~5A)

151.19% 92.95% 193.40% 118.51% 133.09% 142.92% 83.10% 127.20% 123.23%

4. CONCLUSION This paper presented a novel lateral isolator utilizing MREs material for semi-active vibration attenuation, including the successful structural design and experimental verification of the adaptive capacity. The proposed lateral MREs isolator

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adopted the unique laminated structure enabling the large horizontal displacement with tunable lateral stiffness.Performance of the isolator was investigated using an electromagnetic vibration shaker with slip table. Experimental results illustrated that both effective stiffness and equivalent damping of the desired isolator could be triumphantly alterby applying an external electric current up to 140% and 193%, respectively. Besides, the dynamic mechanical propertiesof selected MREs sample was conducted to examine the controllable properties, and the electromagnetic analysis of the isolator was carried out to verify the magnetic circuit design. This work demonstrates the performance of the designedlateral MREs isolator and its potential applications in semi-active vibration isolation in the complex situation.

ACKNOWLEDGMENTSThis work was supported by the National Natural Science Foundation of China (Grant No. 61203098), the National Sci-Tech Support Plan (2012BAF06B04), the Fundamental Research Funds for the Central Universities (Grant No.CDJZR13120090, CDJZR120018). The authors are grateful for the support.

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