A Study on the Tribological Characteristics of a Magneto-Rheological Elasteomer(Journal of...

7/21/2019 A Study on the Tribological Characteristics of a Magneto-Rheological Elasteomer(Journal of Tribology)-Libre

1/5

A Study on the TribologicalCharacteristics of a Magneto-Rheological Elastomer

Deuk-Won Lee

Kwanghee Lee

Chul-Hee Lee1

Department of Mechanical Engineering,

Inha University,

253 Yonghyeon-dong,

Nam-gu, Incheon 402-751, South Korea

e-mail: [email protected].

Cheol-Hyun Kim

Won-Oh Cho

Research and Development Center,

Chang Am LS Company,Asan-City,

ChoongChungNam-Do 336-857, South Korea

Research on the applications of magneto-rheological (MR) elasto-mers in mechanical engineering has greatly expanded, whereasthe performance of MR fluids in tribology has rarely been investi-gated. In this study, the tribological characteristics of an MR elas-tomer are identified in order to improve tribological performancewith the activation of a magnetic field. Microscopic changes inthe surface and in the MR particles are investigated. The frictionand wear of an MR elastomer is measured using a pin-on-disc tes-ter under applied and unapplied magnetic fields. In addition, thelinear sliding friction of an MR elastomer with respect to differentvelocities and loads is measured using a linear sliding tester.[DOI: 10.1115/1.4023080]

Keywords: coefficient of friction, wear, Magneto-rheological(MR) elastomer, magnetic field

1 Introduction

Magneto-rheological (MR) elastomers are in a solid state andconsist of polymers, such as rubber or silicone filled with magnet-izable particles, which are typically sub-micron sized iron par-ticles [1]. The advantage of MR materials is their ability toinstantaneously change their properties such as their elastic modu-lus and stiffness under a magnetic field [2]. Magneto-rheologicalmaterials can be classified into two groups based on the types ofnonmagnetic base material: an MR fluid or an MR elastomer. AnMR fluid is a classical smart material that is used,for example, insuspension systems with micro-sized magnetically polarizableparticles such as carbonyl iron, a carrier liquid such as siliconeoil, and mineral oil. The MR fluid is normally a free-flowing liq-uid with a consistency similar to that of motor oil. Its particlesrandomly disperse and the fluid exhibits Newtonian behavior.Upon activation of an external magnetic field, the fluids resist-ance to motion dramatically increases; thus, it can more

effectively oppose an external force. There have been studies onthe applications and tribological characteristics of the MR fluid[36]. However, there are shortcomings of the MR fluid. Whenthere is a leakage of fluid, it can cause environmental contamina-tion. Additionally, the fluid must be sealed in a confined space inorder to prevent any leakage. Particle residue in the fluid can de-grade the performance. To compensate for these weaknesses, MRelastomers with the same properties as MR fluids [7] have beendeveloped for use in nonconfined spaces.

There has been some research focused on MR elastomers. The

R&D laboratory of Toyota Center developed a silicon gel contain-ing iron particles for engine mounts [8]. The Ford research labora-tory developed MR elastomers with natural and synthetic rubber[9]. Watson used MR elastomers to make tunable automotivebushings [10]. Isolation systems using the properties of MR elas-tomers are proposed. However, although there are a number ofstudies evaluating the performance and applications of MR elasto-mers, hardly any research exists on the evaluation of the tribologi-cal characteristics, such as friction or wear, of MR elastomers.

The particles in an MR fluid have more contact with surfaceswhen they are working in high speed environments because theparticles randomly dispense in the fluid and they can move freely.However, the particles in an MR elastomer are fixed over the basematerial, thus occurrences of contact remains limited compared toin an MR fluid. In addition, the tribological characteristics of anMR elastomer can be controlled under different intensities of

magnetic fields compared with common elastomers. The MR elas-tomers change their properties when a magnetic field is applied.New studies of MR elastomers have been carried out in variousapplication areas, although this research has remained at a basiclevel [11]. Magneto-rheological elastomers have wide-rangingpotential applications. Therefore, the technical skills needed to an-alyze their characteristics and improve their performance must bedeveloped. This study is mainly focused on estimating the frictionand wear characteristics of MR elastomers in a magnetic field.

Experiments are performed to examine the tribological charac-teristics of an MR elastomer made of five different types of mac-romolecule (high polymer) with different viscosities and with Fe,Ni, and Co powders. The results are used to evaluate the linearsliding friction characteristics of the MR elastomer under differentload conditions with and without an applied magnetic field. The

stick-slip phenomenon of the MR elastomer is observed and meas-ured during the linear sliding friction experiment. Stick-slip is aphenomenon caused by a sudden change in friction when two bodiesare in contact. The sliding friction characteristics vary according tothe sliding speed and stick-slip occurs because of the alternationbetween linear sliding friction and dynamic friction. This phenom-enon causes many serious problems in actual situations. For example,vibration caused by stick-slip can decrease precision in industrialmanufacturing processes. Therefore, a great amount of research hasbeen devoted to analyzing this problem [2,12,13].

2 Magneto-Rheological Elastomer

To make an MR elastomer, a silicone gel is composed using ahydrosilylation reaction of a;x-vinyl polydimethylsiloxane and

a;x-hydrido polydimethylsiloxane. Five different macromole-cules (high polymers) of different viscosities and Fe, Ni, and Co

powder are filled with the influence of magnetic polarity. An ad-hesion promoter, such as vinyl trialkoxy silane or hydrogen trial-koxy silane, is added to delay the separation of the mixture andsilicone macromolecule and to couple with each other when thesilicone reaction occurs. As a catalyst, a coordinate number 6 ofplatinic acid and divinyl tetramethyl disiloxane synthesis areadded and adjusted to the proper Pt content. The MR elastomersare poured into a molding box and left at room temperature inorder to eliminate bubbles. A molding box filled with the MRelastomer is placed in an oven for 2 h to harden [1]. The com-pleted MR elastomers are 59.5 mm in diameter and 6 and 15 mmin height, respectively, as shown in Fig.1.

1Corresponding author

Contributed by the Tribology Division of ASME for publication in the J OURNAL

OFT RIBOLOGY. Manuscript received January 20, 2012; final manuscript received July

16, 2012; published online December 20, 2012. Assoc. Editor: George K. Nikas.

Journal of Tribology JANUARY 2013, Vol. 135 / 014501-1CopyrightVC 2013 by ASME

Downloaded 21 Jan 2013 to 165.246.93.54. Redistribution subject to ASME license or copyright; see http://www.asme.org/terms/Terms_Use.cfm


2/5

3 Experiments

A pin-on-disc tester, as shown in Fig. 2, is used to investigatethe friction and wear characteristics of the MR elastomer. Thepin-on-disc tester can switch the magnetic field on and off with aconstant intensity to investigate the friction and wear characteris-

tics. Several experiments are conducted under different test condi-tions with the existence of magnetic fields and various loads.

A linear sliding tester designed to measure linear sliding fric-tion is shown in Fig.3. Since some parts of the original tester aremade of steel, it could be affected by a magnetic field during thetest. Thus, there was a possibility that the test results could beunreliable. Therefore, the tester was re-designed using aluminum,which is not affected by a magnetic field. The tester consists of adata acquisition board for data collection, a linear stage, a powersupply, and an electromagnet with a 60 mm in diameter, 60 mm in

height, and a magnetic field strength of 0.2 T.In the first stage of the test, the surface of the MR elastomer isobserved through a microscope to identify its characteristics, withand without a magnetic field, before carrying out the friction andwear test. The friction and wear characteristics using a pin-on-disctester are then identified. The pin diameter and length used in thetest are 5 and 30 mm, respectively. Because rubber can easily betorn by sharp edges, the experiments are conducted with a steelball attached to the end of the pin to minimize damage to the sur-face of the MR elastomer. Table 1 shows the conditions of thepin-on-disc test according to the existence of a magnetic field; theother test conditions are the same as in the test using rubber. Thevelocity and time duration are fixed at 2.36 mm/s and 2 h, respec-tively. The load is varied (5, 10, and 15N).

In the second stage, a linear sliding test is carried out for an MRelastomer 6 and 15 mm in height and 59.5mm in diameter. Table2

shows the conditions of the test. Two test conditions are used: anapplied magnetic field and with no magnetic field. The appliedloads are 2 and 6 N, and the velocities are 1, 10, and 37.5 mm/s.The sliding distance is fixed at 20 mm.

Fig. 1 The MR elastomer specimens (59.5mm in diameter and6 and 15 mm in height)

Fig. 2 Pin-on-disc tester

Fig. 3 Linear sliding tester

Table 1 Test conditions of pin-on-disc test

Magneticfield

Testnumber

Load(N)

Velocity(mm/s)

Time(h)

Gauss(G)

Unapplied 1 5 2.36 2 02 10 2.36 2 0

3 15 2.36 2 0Applied 4 5 2.36 2 20

5 10 2.36 2 206 15 2.36 2 20

014501-2 / Vol. 135, JANUARY 2013 Transactions of the ASME



3/5

4. Results and Discussion

To identify the characteristics of an MR elastomer with a mag-netic field, the surface is observed using a microscope. Figures4(a)and4(b)are images of the surfaces of the MR elastomer withno applied magnetic field and with an applied magnetic field,respectively. The carbonyl iron (CI) particles are likely to gatherdue to the presence of a magnetic field (compared to no magneticfield), which is shown in Fig. 4(b). The gathered CI particlesassume that a resisting force can be applied to the direction of themagnetic field. The results of the friction and wear characteristics

are shown differently, depending on magnetic field. Based on theresults, a lower coefficient of friction and wear under the magnetic

field show that the stiffness and modulus of the MR elastomershave changed because of the resisting force.A test was conducted in order to identify the changes in the fric-

tion and wear characteristics according to the intensity of the

Table 2 Conditions of linear sliding test

Magneticfield

Testnumber

Velocity(mm/s)

Load(N)

Distance(mm)

Gauss(T)

Unapplied 7 1 2 20 08 1 6 20 09 10 2 20 0

10 10 6 20 011 37.5 2 20 012 37.5 6 20 0

Applied 13 1 2 20 0.214 1 6 20 0.215 10 2 20 0.216 10 6 20 0.217 37.5 2 20 0.218 37.5 6 20 0.2

Fig. 4 Microscopic images on the surface of the MR elastomer:

(a) no magnetic field, and (b) applied magnetic field

Fig. 5 Results of the average friction coefficients based on thepin-on-disc test results

Fig. 6 Images on the surface of the MR elastomer after the pin-on-disc tests: (a) no magnetic field, and (b) applied magneticfield

Journal of Tribology JANUARY 2013, Vol. 135 / 014501-3



4/5

applied magnetic field. The measured friction coefficient datafrom the pin-on-disc test is shown in Fig.5. Tests 1 to 3 are caseswith no magnetic field, whereas Test 4 to Test 6 are cases with amagnetic field. The duration and velocity are fixed at 2 h and2.36 m/s, respectively. The applied load is varied from 5 to 15 N.These results show that a higher friction coefficient occurred withno magnetic field compared to the coefficient with a magnetic field.Additionally, the test shows that a higher load increased the coeffi-cient of friction. Therefore, it is confirmed that the performance

against friction is improved for the case of a lower load and appliedmagnetic field.

In general, Schallamach waves and the generation of wear par-ticles typically occur in elastomers during a friction and wear test[14]. These phenomena also occurred in the MR elastomer duringthe pin-on-disc test in this study because the base material of theMR elastomer is a silicon-based material. The generated Schal-lamach waves and wear particles are shown in Fig. 6. The solidarrow in Fig. 6(a) shows the direction of rotation. In the figure,the Schallamach waves and wear particles are marked in front ofthe arrow. As shown in Fig. 6(b), the Schallamach wave phenom-enon and the generation of wear particles occurred less oftenwhen the stiffness increased with the activation of the magneticfield.

In the second experiment, a linear sliding test was carried out inorder to investigate the characteristics of linear sliding friction inan MR elastomer. Figure7shows the measured linear sliding fric-tion coefficient for different test conditions, which are describedin Table2. Figure7 shows that the friction coefficient at the be-ginning of the test rapidly increases. The MR elastomer is com-pressed at the beginning of the test because of the load applied to

its surface, which caused a sudden increase in the coefficient offriction for the initial state of the test. Tests 7 to 12 are cases with

Fig. 7 Results of the linear sliding test: (a) velocity51 mm/s,(b) velocity510 mm/s, and (c) velocity537.5mm/s

Fig. 8 Comparison of the results between linear sliding fric-tion and acceleration (load of 2 N and velocity of 1 mm/s; Test 7)

Fig. 9 Average friction coefficient results from the linear slid-ing test

014501-4 / Vol. 135, JANUARY 2013 Transactions of the ASME



5/5

no magnetic field, whereas Tests 13 to 18 are cases with anapplied magnetic field. The stick-slip phenomenon is detectedfrom the results of the linear sliding friction test. Figure 7 showsthat as the velocity increases, the effect of the stick-slip phenom-enon decreases. The stick-slip phenomenon in Test 7 with nomagnetic field is the most prominent. As shown in Fig. 8, theacceleration data and the coefficient of friction are compared andanalyzed using Test 7 to determine if the observed phenomenoncould be considered to be stick-slip behavior. Since the magnitudeand period in the frequency of the vibration acceleration during

sliding almost coincides with those of the friction coefficient, it isconfirmed that stick-slip occurred in the MR elastomer. As shownby the test results, the incidence of stick-slip decreases when amagnetic field is applied. Therefore, it is suggested that the inci-dence of stick-slip depends on the magnetic field because themagnetic field changes the stiffness of the MR elastomer. Figure 9shows the average results of the measured friction coefficient inthe steady state, which is from a distance of 8 to 14 mm. Theincreased load and velocity and the unapplied magnetic field inthe test show the result of a higher coefficient of friction. In thelinear sliding friction test with a short duration and a small load,Schallamach waves and wear particles are not generated.

5 Conclusion

The tribological characteristics of MR elastomers are exam-

ined. Magneto-rheological elastomers, based on silicone rubbermixed with high polymers with two different viscosities and po-larity materials, are produced. Friction and wear tests were carriedout to obtain the tribological characteristics under a magneticfield. Microscopic images of the surface of the MR elastomersshow that CI particles are likely to gather when a magnetic field isapplied. The gathered CI particles can change the property, suchas the modulus of MR elastomers, affecting the friction and wearcharacteristics of MR elastomers. The friction and wear character-istics of the elastomer are measured using a pin-on-disc tester. Toexamine the performance against friction and wear, the tests areconducted under an applied magnetic field and with no magneticfield with three load conditions. The results of the pin-on-disctests shows that a smaller load with an applied magnetic fieldleads to a decrease of the friction coefficient. In addition, it wasobserved that Schallamach waves and wear particles are generatedon the surface of the MR elastomer, especially when no magneticfield is applied. Schallamach waves are different from the ones incommon elastomers due to the CI particles. It is assumed that theCI particles affect the elasticity of MR elastomers. Schallamachwaves are not observed when a magnetic field is applied becausethe MR elastomer stiffens.

A linear sliding tester was designed and the test was conductedin order to evaluate the friction and wear characteristics of theMR elastomer under the applied magnetic field. The results of thelinear sliding test show a lower friction force when a smaller loadand slower velocity are applied. In addition, a stick-slip phenomenon

is detected when measuring linear sliding friction and the stick-slip behavior decreases when the magnetic field is activated. Theincreased velocity can also diminish the stick-slip effect. Basedon the obtained tribological characteristics, including the stick-slip phenomenon, MR elastomers could potentially be applied tovarious industrial or automotive systems with further studiesunder more realistic conditions. Applications using MR elasto-mers can be specified to, for example, a controllable pad attachedto the bottom of a robot or clutches with a controllable pad onthem. Further studies need to be conducted under more realistic

conditions.

Acknowledgment

This research was supported by the Ministry of KnowledgeEconomy (MKE), Korea, under the Convergence InformationTechnology Research Center (CITRC) support program (GrantNo. NIPA-2012-H0401-12-1007) supervised by the National ITIndustry Promotion Agency (NIPA). This research is also sup-ported by the Basic Science Research Program of the NationalResearch Foundation of Korea (NRF), funded by the Ministry ofEducation, Science and Technology of the government of Korea(Grant No. 2010-0025763). This research was supported by InhaUniversity.

References[1] Shen, Y., Golnarachi, M. F., and Heppler, G. R., 2004, Experimental Research

and Modeling of Magnetorheological Elastomers,J. Intell. Mater. Syst. Struct.,

15, pp. 2735.[2] Deng, H. X., and Gong, X. L., 2008, Application of Magnetorheological Elas-

tomer to Vibration Absorber, Commun. Nonlinear Sci. Numer. Simul., 13, pp.19381947.

[3] Lee, C.-H., and Jang, M.-G., 2011, Virtual Surface Characteristics of a Tactile

Display Using Magneto-Rheological Fluid,Sensors,11(3), pp. 28452856.[4] Lee, C.-H., Lee, D. W., Choi, J. Y., Choi, S. B., Cho, W. O., and Yun, H. C.,

Tribological Characteristics Modification of Magnetorheological Fluid,

ASME J. Tribol., 133, p. 031801.[5] Wong, P. L., Bullough, W. A., Feng, C., and Lingard, S., 2001, Tribological

Performance of a Magneto-Rheological Suspension,Wear,247, pp. 3340.[6] Li, W. H., and Zhang, X. Z., 2008, The Effect of Friction on Magnetorheologi-

cal Fluids, Korea-Aust. Rheol. J.,20(2), pp. 4550.

[7] Carlson, J. D., 1991, U.S. Patent No. 5,054,593.[8] Shiga, A., Fujimoto, Y., and Hirose, M., 1993, Tokai Hei Japanese Patent 5-

25315.

[9] Ginder, J. M., Nichols, M. E., Elie, L. D., and Clark, S. M., 2000, Controlla-ble-Stiffness Components Based on Magnetorheological Elastomers, Proc.

SPIE,3985, pp. 418425.[10] Watson, J. R., 1996, U.S. Patent No. 05,609,353.

[11] Zhou, G. Y., 2003, Shear Properties of a Magnetorheological Elastomer,

Smart Mater. Struct.,12, pp. 139146.[12] Maegawa, S. and Nakano K., 2010, Mechanism of Stick-Slip Associated With

Schallamach Waves,Wear,268, pp. 924930.[13] De Baets, P., Degrieck, J., Van De Velde, F., and Van Peteghem, A. P., 2000,

Experimental Verification of the Mechanisms Causing Stick-Slip Motion Orig-

inating From Relative Deceleration,Wear,243, pp. 4959.[14] Fukahori, Y., Gabriel, P., and Bushfield, J. J. C., 2010, How Does Rubber

Truly Slide Between Schallamach Waves and Stick-Slip Motion?, Wear, 269,pp. 854866.

Journal of Tribology JANUARY 2013, Vol. 135 / 014501-5
http://dx.doi.org/10.1177/1045389X04039264http://dx.doi.org/10.1016/j.cnsns.2007.03.024http://dx.doi.org/10.3390/s110302845http://dx.doi.org/10.3390/s110302845http://dx.doi.org/10.1016/S0043-1648(00)00507-Xhttp://dx.doi.org/10.1117/12.388844http://dx.doi.org/10.1117/12.388844http://dx.doi.org/10.1117/12.388844http://dx.doi.org/10.1088/0964-1726/12/1/316http://dx.doi.org/10.1088/0964-1726/12/1/316http://dx.doi.org/10.1016/j.wear.2009.12.018http://dx.doi.org/10.1016/S0043-1648(00)00428-2http://dx.doi.org/10.1016/j.wear.2010.08.016http://dx.doi.org/10.1016/j.wear.2010.08.016http://dx.doi.org/10.1016/S0043-1648(00)00428-2http://dx.doi.org/10.1016/j.wear.2009.12.018http://dx.doi.org/10.1088/0964-1726/12/1/316http://dx.doi.org/10.1117/12.388844http://dx.doi.org/10.1117/12.388844http://dx.doi.org/10.1016/S0043-1648(00)00507-Xhttp://dx.doi.org/10.3390/s110302845http://dx.doi.org/10.1016/j.cnsns.2007.03.024http://dx.doi.org/10.1177/1045389X04039264

A Study on the Tribological Characteristics of a Magneto-Rheological Elasteomer(Journal of...

Documents

Transcript of A Study on the Tribological Characteristics of a Magneto-Rheological Elasteomer(Journal of...