Proceedings of the ASME 2009 Conference on Smart Materials, Adaptive Structures and Intelligent Systems SMASIS2009 September 20-24, 2009, Oxnard, California, USA SMASIS2009-1310 DEFINING AND INVESTIGATING NEW SYMMETRY CLASSES FOR THE NEXT GENERATION OF MAGNETORHEOLOGICAL ELASTOMERS Paris R. von Lockette, Rowan University Samuel Lofland, Rowan University Joseph Biggs, Rowan University 1 Copyright 2009 by ASME
ABSTRACT This work addresses the fundamental difference in behavior between magnetorheological elastomers (MREs) formed from soft-magnetic particles, whose behavior is driven by local demagnetizing effects and those formed with hard-magnetic particles that have a preferred magnetic axis and therefore generate magnetic torques at the particle level. This work explores the phenomena by defining and examining four classes of MREs based upon permutations of particle alignment - magnetization pairs, i.e. I-I for magnetically isotropic particles arranged isotropically (randomly, or unaligned), A-A for magnetically anisotropic particles arranged anisotropically (typically aligned in chains), etc. The distinctions are important since the particle-field interactions for each class differ substantially. The behavior of classes I-I and I-A are driven primarily by demagnetizing effects while classes I-A and A-A are driven by the torques produced in the particles.mre materials made with barium hexaferrite (BaM) (Classes A-A and I-A) and Fe powders (Classes A-I and I-I), aligned and unaligned, served as proxies for each of the four classes in this work. BaM, with saturation magnetization M sat = 4 10 5 A/m and coercive field H c > 3 10 5 A/m, provided the magnetically anisotropic behavior while iron, with M sat =1.8 10 6 A/m and H c < 2 10^3 A/m, provided the soft magnetic behavior. Experiments on materials with 30% particle concentrations showed that under uniform magnetic fields class A-A (aligned BaM) MREs were capable of large deflections in cantilever beam bending (deflections of 12mm for length 50mm and magnetic field 1.2 10 5 A/m) whereas all other classes, including I-A (random BaM) MREs, showed none. Tip deflection varied linearly with applied field strength. Tip blocking-force versus deflection experiments were also conducted on cantilevered A-A specimens. These tests showed that tip force increased with decreasing free deflection and with increasing field strength. INTRODUCTION Magnetorheological elastomers (MREs) are a novel class of smart materials, comprised of magnetic particles in a non-magnetic rubbery matrix, which have gained renewed interest recently [1,2,3,4,5,6,7,8]. MREs are able to change Figure 1: Current literature on MRE behavior ascribes shear-stiffening behavior of MREs to the resistance of long chains of particles to shear deformation with respect to the applied magnetic field axis, H. their apparent shear stiffness under the influence of a magnetic field which has many controls applications including tunable vibration absorbers and active bushings[9,10]. Existing literature in the field generally ascribes the shear-stiffening behavior of MREs to the resistance of long chains of particles, formed while curing the material within a magnetic field of 1-2 MA/m, to deformation with respect to the magnetic field axis [11]. (See Figure 1). The perturbation of these chains drives the particles away from their preferred minimum energy state, thereby inducing an internal restorative force [12]. While it is true that the minimum energy state for a chain of particles is aligned with the external field, an examination of the driving magnetic phenomena at the particle level revels that soft- and hard-magnetic materials will behave substantially differently. The torque T acting on an individual particle is determined by T = M H where M is the magnetization of the particle and H the applied magnetic field. For soft-magnetic materials, such as iron, M aligns with H yielding T = 0 whereas for hardmagnetic materials M is independent of H such that generally T 0. The focus of this work is the examination of the resulting difference in behavior between materials made from hard- and soft-magnetic filler particles. Figure 2: Four classes of MRE materials as described by particle alignmentmagnetization pairs. Ellipses show magnetization axes. 2 Copyright 2009 by ASME
Magnetic filler particles may be classified as either anisotropic (A, hard-magnetic) or isotropic (I, soft-magnetic), defining two classifications based on particle magnetization. Additionally, particle arrangements provide two class distinctions: anisotropic for particles arranged in chains or isotropic for particles arranged randomly with no order. Together, this distinction yields a four classificationa of particles based on alignment-magnetization pairs, namely I-I, A-I, I-A, and A-A (Figure 2). EXPERIMENTAL METHODS For this work nominally 40-micron iron (Fe) particles served as the soft-magnetic filler particles (coercive fiels μ 0 H c < 2.5 mt) while nominally 40 micron M-type barium hexaferrite (BaM) particles served as the hard-magnetic filler (μ 0 H c > 0.4 T). Material classes A-A and A-I were produced by curing in μ 0 H ~ 2 T to produce anisotropy in particle arrangements while material classes I-I and I-A were cured as mixed in Earth s field. Dow Corning HS II silicone elastomer compound was used as the matrix material in a 30% v/v particle to matrix ratio. Figure 4: Class A A (BaM) sample 5 x 20 x 75 mm under 150 T. Graph paper scale is ¼ in. Class A A (shown) deforms while Classes A I, I A, and I I do not (not shown). RESULTS During the free cantilever bending test, only samples of class A-A showed deformation under a magnetic field. Figure 4 shows the deformed shape of the A-A sample at 0 H = 0.15 T. The tip deformation was linear with respect to field strength (Fig. 5). Figure 3: Schematic of cantilever bending experiment showing C shaped electromagnet, MRE sample with class poling direction (red), and magnetic flux direction (blue). A cantilever actuation test measuring the field dependence of the tip deflection was conducted on samples from all four classes using a C-shaped electromagnet as shown schematically in Figure 3. All samples had dimension 5 20 75 mm 3 where 75 mm was the free cantilever length. The displacement was measured using an optical microscope, and the field strength was measured with a Lakeshore Gaussmeter. In addition, A blocking force test was conducted on the class A-A sample by placing a Shimpo model FGV-0.5x force gauge at specified distances from its tip. The sample was allowed to free deform until it contacted the force transducer which measured the applied force. Figure 5: Tip deflection versus field strength for class A-A sample in free cantilever bending experiment of Figure 3. Material classes A-I, I-I, and I-A showed no deformation for the range of field strengths tested. The blocking force test of the sample of class A-A (Fig. 6) showed an increase in force with increasing field strength and a decrease in force with increasing tip deflection. 3 Copyright 2009 by ASME
Figure 6: Blocking force vs. field applied strength at tip deflections shown for cantilever testing of class A-A (BaM) materials CONCLUSIONS The results presented show clear differences in behavior between the class A-A and classes A-I, I-I, and I-A samples. Class A-A samples produce actuation in cantilever bending whereas the other classes do not. No tip deflection was produced even in samples composed of the same magnetic filler particles, BaM, when particle arrangements were isotropic, class I-A. The lack of actuation in materials having the same BaM magnetic filler highlights the dual dependence on both particle magnetization and particle arrangement. One interpretation for class I-A (BaM) materials, is that while the individual particles have internal magnetization, their random arrangement yields zero net magnetization of the bulk and hence no internal torque en masse. An alternative view is that the individual torques generated at the particle level cancel and therefore generate no bulk response. The lack of actuation in classes I-I and A-I (Fe) materials supports the assertion that the soft-magnetic behavior of iron particles, regardless of alignment, yields no magnetic torque and thereby cannot generate an internal moment to cause deflection of the sample. The results of Figure 6 show the ability of the class A-A samples to do work further highlighting the difference between class A-A and the other classes. [3] David York, Xiaojie Wang, and Faramarz Gordaninejad, A new MR fluid elastomer vibration isolator, J. Intell. Mater. Syst. Struct. 18, 1221 (2007). [4] Hua xia Deng and Xing long Gong, Application of magnetorheological elastomer to vibration absorber, Communications in Nonlinear Science and Numerical Simulation, 13, 1938 (2008). [5] A. Albanese Lerner and K.A Cunefare, Performance of MRE based vibration absorbers, Intell. Mater. Syst. Struct. 19, 551 (2008). [6] Saul Opie and Yim Woosoon, A tunable vibration isolator using a magnetorheological elastomer with a field induced modulus bias, Proceedings of the ASME International Mechanical Engineering Congress and Exposition, IMECE 2007, 99 (2008). [7] G.Y. Zhou, and Q. Wang, Q. Use of magnetorheological elastomer in an adaptive sandwich beam with conductive skins. Part I: Magnetoelastic loads in conductive skins, Inter. J. Solids Struct. 43, 5386 (2006). [8]G.Y. Zhou, and Q. Wang, Magnetorheological elastomerbased smart sandwich beams with nonconductive skins, Smart Mater. Struct., 14, 1001 2005, p 1001 1009 [9] G Y Zhou Shear properties of a magnetorheological elastomer, Smart Mater. Struct. 12 139 146 (2002) [10] Hua Xia Gong Deng, Wang Xing Long, and Lian Hua, Development of an adaptive tuned vibration absorber with magnetorheological elastomer, Smart Mater. Struct. 15, p N111 16 (2006). [11] L Chen, X L Gong, W H Li, Microstructures and viscoelastic properties of anisotropic magnetorheological elastomers, Smart Mater. Struct. 16 p 2645 50 (2007) [12] Y Shen, M F Golnaraghi, G R Heppler, Experimental Research and Modeling of Magnetorheological Elastomers, Journal of Intelligent Material Systems and Structures 15 p 27 35 (2004) ACKNOWLEDGEMENTS The authors would like to thank several students for their support: William Hargrave, Rocco Bravaco, Kevin Anderson, Taylor Kirk, Sean Meehan, Joseph Urcinas. REFERENCES [1] T. Lindroos, S. Aalto, E. Jarvinen, T. Karna, M. Meinander, and T. Kallio, Dynamic compression testing of a tunable spring element consisting of a magnetorheological elastomer, Smart Mater. Struct. 16, 506 (2004). [2]G.Y. Zhou, and Q. Wang, Magnetorheological elastomerbased smart sandwich beams with nonconductive skins, Smart Mater. Struct., 14, 1001 2005, p 1001 1009 4 Copyright 2009 by ASME
1 T. Lindroos, S. Aalto, E. Jarvinen, T. Karna, M. Meinander, and T. Kallio, Dynamic compression testing of a tunable spring element consisting of a magnetorheological elastomer, Smart Mater. Struct. 16, 506 (2004). 2 G.Y. Zhou, and Q. Wang, Magnetorheological elastomer based smart sandwich beams with nonconductive skins, Smart Mater. Struct., 14, 1001 2005, p 1001 1009 3 David York, Xiaojie Wang, and Faramarz Gordaninejad, A new MR fluid elastomer vibration isolator, J. Intell. Mater. Syst. Struct. 18, 1221 (2007). 4 Hua xia Deng and Xing long Gong, Application of magnetorheological elastomer to vibration absorber, Communications in Nonlinear Science and Numerical Simulation, 13, 1938 (2008). 5 A. Albanese Lerner and K.A Cunefare, Performance of MRE based vibration absorbers, Intell. Mater. Syst. Struct. 19, 551 (2008). 6 Saul Opie and Yim Woosoon, A tunable vibration isolator using a magnetorheological elastomer with a field induced modulus bias, Proceedings of the ASME International Mechanical Engineering Congress and Exposition, IMECE 2007, 99 (2008). 7 G.Y. Zhou, and Q. Wang, Q. Use of magnetorheological elastomer in an adaptive sandwich beam with conductive skins. Part I: Magnetoelastic loads in conductive skins, Inter. J. Solids Struct. 43, 5386 (2006). 8 G.Y. Zhou, and Q. Wang, Magnetorheological elastomer based smart sandwich beams with nonconductive skins, Smart Mater. Struct., 14, 1001 2005, p 1001 1009 9 G Y Zhou Shear properties of a magnetorheological elastomer, Smart Mater. Struct. 12 139 146 (2002) 10 Hua Xia Gong Deng, Wang Xing Long, and Lian Hua, Development of an adaptive tuned vibration absorber with magnetorheological elastomer, Smart Mater. Struct. 15, p N111 16 (2006). 11 L Chen, X L Gong, W H Li, Microstructures and viscoelastic properties of anisotropic magnetorheological elastomers, Smart Mater. Struct. 16 p 2645 50 (2007) 12 Y Shen, M F Golnaraghi, G R Heppler, Experimental Research and Modeling of Magnetorheological Elastomers, Journal of Intelligent Material Systems and Structures 15 p 27 35 (2004) 5 Copyright 2009 by ASME